Table of Contents
- 6.1 The MySQL Server
- 6.1.1 Server Option and Variable Reference
- 6.1.2 Server Configuration Defaults
- 6.1.3 Server Command Options
- 6.1.4 Server System Variables
- 6.1.5 Using System Variables
- 6.1.6 Server Status Variables
- 6.1.7 Server SQL Modes
- 6.1.8 IPv6 Support
- 6.1.9 Server-Side Help
- 6.1.10 Server Response to Signals
- 6.1.11 The Server Shutdown Process
- 6.2 The MySQL Data Directory
- 6.3 The mysql System Database
- 6.4 MySQL Server Logs
- 6.5 MySQL Server Plugins
- 6.6 Running Multiple MySQL Instances on One Machine
- 6.7 Tracing mysqld Using DTrace
MySQL Server (mysqld) is the main program that does most of the work in a MySQL installation. This chapter provides an overview of MySQL Server and covers general server administration:
Server configuration
The data directory, particularly the
mysqlsystem databaseThe server log files
Management of multiple servers on a single machine
For additional information on administrative topics, see also:
- 6.1.1 Server Option and Variable Reference
- 6.1.2 Server Configuration Defaults
- 6.1.3 Server Command Options
- 6.1.4 Server System Variables
- 6.1.5 Using System Variables
- 6.1.6 Server Status Variables
- 6.1.7 Server SQL Modes
- 6.1.8 IPv6 Support
- 6.1.9 Server-Side Help
- 6.1.10 Server Response to Signals
- 6.1.11 The Server Shutdown Process
mysqld is the MySQL server. The following discussion covers these MySQL server configuration topics:
Startup options that the server supports. You can specify these options on the command line, through configuration files, or both.
Server system variables. These variables reflect the current state and values of the startup options, some of which can be modified while the server is running.
Server status variables. These variables contain counters and statistics about runtime operation.
How to set the server SQL mode. This setting modifies certain aspects of SQL syntax and semantics, for example for compatibility with code from other database systems, or to control the error handling for particular situations.
The server shutdown process. There are performance and reliability considerations depending on the type of table (transactional or nontransactional) and whether you use replication.
For listings of MySQL server variables and options that have been added, deprecated, or removed in MySQL 5.7, see Section 1.5, “Server and Status Variables and Options Added, Deprecated, or Removed in MySQL 5.7”.
Not all storage engines are supported by all MySQL server binaries and configurations. To find out how to determine which storage engines your MySQL server installation supports, see Section 14.7.5.16, “SHOW ENGINES Syntax”.
The following table provides a list of all the command line
options, server and status variables applicable within
mysqld.
The table lists command-line options (Cmd-line), options valid in configuration files (Option file), server system variables (System Var), and status variables (Status var) in one unified list, with notification of where each option/variable is valid. If a server option set on the command line or in an option file differs from the name of the corresponding server system or status variable, the variable name is noted immediately below the corresponding option. For status variables, the scope of the variable is shown (Scope) as either global, session, or both. Please see the corresponding sections for details on setting and using the options and variables. Where appropriate, a direct link to further information on the item as available.
For a version of this table that is specific to MySQL Cluster, see Section 19.3.2.5, “MySQL Cluster mysqld Option and Variable Reference”.
Table 6.1 Option/Variable Summary
The MySQL server has many operating parameters, which you can change at server startup using command-line options or configuration files (option files). It is also possible to change many parameters at runtime. For general instructions on setting parameters at startup or runtime, see Section 6.1.3, “Server Command Options”, and Section 6.1.4, “Server System Variables”.
Before MySQL 5.7.5, on Unix platforms,
mysql_install_db creates a default option file
named my.cnf in the base installation
directory. This file is created from a template included in the
distribution package named my-default.cnf.
You can find the template in or under the base installation
directory. When started using mysqld_safe, the
server uses my.cnf file by default. If
my.cnf already exists,
mysql_install_db assumes it to be in use and
writes a new file named my-new.cnf instead.
With one exception, the settings in the default option file are
commented and have no effect. The exception is that the file sets
the sql_mode system variable to
NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES.
This setting produces a server configuration that results in
errors rather than warnings for bad data in operations that modify
transactional tables. See Section 6.1.7, “Server SQL Modes”.
On Windows, MySQL Installer interacts with the user and creates a
file named my.ini in the base installation
directory as the default option file. If you install on Windows
from a Zip archive, you can copy the
my-default.ini template file in the base
installation directory to my.ini and use the
latter as the default option file.
On Windows, the .ini or
.cnf option file extension might not be
displayed.
On any platform, after completing the installation process, you
can edit the default option file at any time to modify the
parameters used by the server. For example, to use a parameter
setting in the file that is commented with a #
character at the beginning of the line, remove the
#, and modify the parameter value if necessary.
To disable a setting, either add a # to the
beginning of the line or remove it.
For additional information about option file format and syntax, see Section 5.2.6, “Using Option Files”.
When you start the mysqld server, you can specify program options using any of the methods described in Section 5.2.3, “Specifying Program Options”. The most common methods are to provide options in an option file or on the command line. However, in most cases it is desirable to make sure that the server uses the same options each time it runs. The best way to ensure this is to list them in an option file. See Section 5.2.6, “Using Option Files”. That section also describes option file format and syntax.
mysqld reads options from the
[mysqld] and [server]
groups. mysqld_safe reads options from the
[mysqld], [server],
[mysqld_safe], and
[safe_mysqld] groups.
mysql.server reads options from the
[mysqld] and [mysql.server]
groups.
An embedded MySQL server usually reads options from the
[server], [embedded], and
[
groups, where xxxxx_SERVER]xxxxx is the name of the
application into which the server is embedded.
mysqld accepts many command options. For a brief summary, execute mysqld --help. To see the full list, use mysqld --verbose --help.
The following list shows some of the most common server options. Additional options are described in other sections:
Options that affect security: See Section 7.1.4, “Security-Related mysqld Options and Variables”.
SSL-related options: See Section 7.4.5, “Command Options for Secure Connections”.
Binary log control options: See Section 6.4.4, “The Binary Log”.
Replication-related options: See Section 18.1.6, “Replication and Binary Logging Options and Variables”.
Options for loading plugins such as pluggable storage engines: See Section 6.5.2, “Installing and Uninstalling Plugins”.
Options specific to particular storage engines: See Section 15.14, “InnoDB Startup Options and System Variables” and Section 16.2.1, “MyISAM Startup Options”.
Some options control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to an option that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server will adjust a value upward. For example, if you assign a value of 0 to an option for which the minimal value is 1024, the server will set the value to 1024.
Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.
Some options take file name values. Unless otherwise specified,
the default file location is the data directory if the value is a
relative path name. To specify the location explicitly, use an
absolute path name. Suppose that the data directory is
/var/mysql/data. If a file-valued option is
given as a relative path name, it will be located under
/var/mysql/data. If the value is an absolute
path name, its location is as given by the path name.
You can also set the values of server system variables at server
startup by using variable names as options. To assign a value to a
server system variable, use an option of the form
--.
For example, var_name=value--key_buffer_size=32M
sets the key_buffer_size variable
to a value of 32MB.
When you assign a value to a variable, MySQL might automatically correct the value to stay within a given range, or adjust the value to the closest permissible value if only certain values are permitted.
If you want to restrict the maximum value to which a variable can
be set at runtime with
SET, you
can define this by using the
--maximum-
command-line option.
var_name=value
You can change the values of most system variables for a running
server with the
SET
statement. See Section 14.7.4, “SET Syntax”.
Section 6.1.4, “Server System Variables”, provides a full description for all variables, and additional information for setting them at server startup and runtime. Section 9.12.2, “Tuning Server Parameters”, includes information on optimizing the server by tuning system variables.
--help,-?Command-Line Format --helpDisplay a short help message and exit. Use both the
--verboseand--helpoptions to see the full message.-
Command-Line Format --allow-suspicious-udfsPermitted Values Type booleanDefault FALSEThis option controls whether user-defined functions that have only an
xxxsymbol for the main function can be loaded. By default, the option is off and only UDFs that have at least one auxiliary symbol can be loaded; this prevents attempts at loading functions from shared object files other than those containing legitimate UDFs. See Section 26.4.2.6, “UDF Security Precautions”. -
Command-Line Format --ansiUse standard (ANSI) SQL syntax instead of MySQL syntax. For more precise control over the server SQL mode, use the
--sql-modeoption instead. See Section 1.8, “MySQL Standards Compliance”, and Section 6.1.7, “Server SQL Modes”. --basedir=,dir_name-bdir_nameCommand-Line Format --basedir=dir_nameSystem Variable Name basedirVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe path to the MySQL installation directory. All paths are usually resolved relative to this directory.
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Command-Line Format --big-tablesSystem Variable Name big_tablesVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault OFFEnable large result sets by saving all temporary sets in files. This option prevents most “table full” errors, but also slows down queries for which in-memory tables would suffice. Since MySQL 3.23.2, the server is able to handle large result sets automatically by using memory for small temporary tables and switching to disk tables where necessary.
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Command-Line Format --bind-address=addrSystem Variable Name bind_addressVariable Scope Global Dynamic Variable No Permitted Values Type stringDefault *The MySQL server listens on a single network socket for TCP/IP connections. This socket is bound to a single address, but it is possible for an address to map onto multiple network interfaces. To specify an address, use the
--bind-address=option at server startup, whereaddraddris an IPv4 or IPv6 address or a host name. Ifaddris a host name, the server resolves the name to an IP address and binds to that address.The server treats different types of addresses as follows:
If the address is
*, the server accepts TCP/IP connections on all server host IPv6 and IPv4 interfaces if the server host supports IPv6, or accepts TCP/IP connections on all IPv4 addresses otherwise. Use this address to permit both IPv4 and IPv6 connections on all server interfaces. This value is the default.If the address is
0.0.0.0, the server accepts TCP/IP connections on all server host IPv4 interfaces.If the address is
::, the server accepts TCP/IP connections on all server host IPv4 and IPv6 interfaces.If the address is an IPv4-mapped address, the server accepts TCP/IP connections for that address, in either IPv4 or IPv6 format. For example, if the server is bound to
::ffff:127.0.0.1, clients can connect using--host=127.0.0.1or--host=::ffff:127.0.0.1.If the address is a “regular” IPv4 or IPv6 address (such as
127.0.0.1or::1), the server accepts TCP/IP connections only for that IPv4 or IPv6 address.
If you intend to bind the server to a specific address, be sure that the
mysql.usergrant table contains an account with administrative privileges that you can use to connect to that address. Otherwise, you will not be able to shut down the server. For example, if you bind the server to*, you can connect to it using all existing accounts. But if you bind the server to::1, it accepts connections only on that address. In that case, first make sure that the'root'@'::1'account is present in themysql.usertable so you can still connect to the server to shut it down. --binlog-format={ROW|STATEMENT|MIXED}Command-Line Format --binlog-format=formatSystem Variable Name binlog_formatVariable Scope Global, Session Dynamic Variable Yes Permitted Values (<= 5.7.6) Type enumerationDefault STATEMENTValid Values ROWSTATEMENTMIXEDPermitted Values (>= 5.7.7) Type enumerationDefault ROWValid Values ROWSTATEMENTMIXEDSpecify whether to use row-based, statement-based, or mixed replication. Statement-based is the default in MySQL 5.7. See Section 18.2.1, “Replication Formats”.
Under some conditions, changing this variable at runtime is not possible, or causes replication to fail. See Section 6.4.4.2, “Setting The Binary Log Format”, for more information.
Setting the binary logging format without enabling binary logging sets the
binlog_formatglobal system variable and logs a warning.-
Deprecated 5.7.6 Command-Line Format --bootstrapThis option is used by the mysql_install_db program to create the MySQL privilege tables without having to start a full MySQL server.
Notemysql_install_db is deprecated as of MySQL 5.7.6 because its functionality has been integrated into mysqld, the MySQL server. Consequently, the
--bootstrapserver option that mysql_install_db passes to mysqld is also deprecated. To initialize a MySQL installation as of MySQL 5.7.6, invoke mysqld with the--initializeor--initialize-insecureoption. For more information, see Section 2.10.1.1, “Initializing the Data Directory Manually Using mysqld”. mysql_install_db and the--bootstrapserver option will be removed in a future MySQL release.--bootstrapis mutually exclusive with--daemonize,--initialize, and--initialize-insecure.In MySQL 5.7.8 and later global transaction identifiers (GTIDs) are not disabled when
--bootstrapis used. Before MySQL 5.7.8, GTIDs were automatically disabled whenever--bootstrapwas used (Bug #20980271). See Section 18.1.3, “Replication with Global Transaction Identifiers”.When the server operates in bootstap mode, some functionality is unavailable that limits the statements permitted in any file named by the
--init-fileoption. For more information, see the description of that option. In addition, thedisabled_storage_enginessystem variable has no effect. -
Command-Line Format --character-sets-dir=dir_nameSystem Variable Name character_sets_dirVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe directory where character sets are installed. See Section 11.5, “Character Set Configuration”.
--character-set-client-handshakeCommand-Line Format --character-set-client-handshakePermitted Values Type booleanDefault TRUEDo not ignore character set information sent by the client. To ignore client information and use the default server character set, use
--skip-character-set-client-handshake; this makes MySQL behave like MySQL 4.0.--character-set-filesystem=charset_nameCommand-Line Format --character-set-filesystem=nameSystem Variable Name character_set_filesystemVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringDefault binaryThe file system character set. This option sets the
character_set_filesystemsystem variable.--character-set-server=,charset_name-Ccharset_nameCommand-Line Format --character-set-serverSystem Variable Name character_set_serverVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringDefault latin1Use
charset_nameas the default server character set. See Section 11.5, “Character Set Configuration”. If you use this option to specify a nondefault character set, you should also use--collation-serverto specify the collation.--chroot=,dir_name-rdir_nameCommand-Line Format --chroot=dir_namePermitted Values Type directory namePut the mysqld server in a closed environment during startup by using the
chroot()system call. This is a recommended security measure. Use of this option somewhat limitsLOAD DATA INFILEandSELECT ... INTO OUTFILE.--collation-server=collation_nameCommand-Line Format --collation-serverSystem Variable Name collation_serverVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringDefault latin1_swedish_ciUse
collation_nameas the default server collation. See Section 11.5, “Character Set Configuration”.-
Command-Line Format --consolePlatform Specific Windows (Windows only.) Write error log messages to
stderrandstdouteven if--log-erroris specified. mysqld does not close the console window if this option is used.If both
--log-errorand--consoleare specified,--consoletakes precedence. The server writes to the console, but not to the log file. (In MySQL 5.5 and 5.6, the precedence is reversed:--log-errorcauses--consoleto be ignored.) -
Command-Line Format --core-filePermitted Values Type booleanDefault OFFWrite a core file if mysqld dies. The name and location of the core file is system dependent. On Linux, a core file named
core.is written to the current working directory of the process, which for mysqld is the data directory.pidpidrepresents the process ID of the server process. On OS X, a core file namedcore.is written to thepid/coresdirectory. On Solaris, use the coreadm command to specify where to write the core file and how to name it.For some systems, to get a core file you must also specify the
--core-file-sizeoption to mysqld_safe. See Section 5.3.2, “mysqld_safe — MySQL Server Startup Script”. On some systems, such as Solaris, you do not get a core file if you are also using the--useroption. There might be additional restrictions or limitations. For example, it might be necessary to execute ulimit -c unlimited before starting the server. Consult your system documentation. -
Introduced 5.7.6 Command-Line Format --daemonize[={OFF|ON}]Permitted Values Type booleanDefault OFFThis option causes the server to run as a traditional, forking daemon, permitting it to work with operating systems that use systemd for process control. For more information, see Section 2.5.10, “Managing MySQL Server with systemd”.
--daemonizeis mutually exclusive with--bootstrap,--initialize, and--initialize-insecure. --datadir=,dir_name-hdir_nameCommand-Line Format --datadir=dir_nameSystem Variable Name datadirVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe path to the data directory.
--debug[=,debug_options]-# [debug_options]Command-Line Format --debug[=debug_options]System Variable Name debugVariable Scope Global, Session Dynamic Variable Yes Permitted Values (Unix) Type stringDefault d:t:i:o,/tmp/mysqld.tracePermitted Values (Windows) Type stringDefault d:t:i:O,\mysqld.traceIf MySQL is configured with the
-DWITH_DEBUG=1CMake option, you can use this option to get a trace file of what mysqld is doing. A typicaldebug_optionsstring isd:t:o,. The default isfile_named:t:i:o,/tmp/mysqld.traceon Unix andd:t:i:O,\mysqld.traceon Windows.Using
-DWITH_DEBUG=1to configure MySQL with debugging support enables you to use the--debug="d,parser_debug"option when you start the server. This causes the Bison parser that is used to process SQL statements to dump a parser trace to the server's standard error output. Typically, this output is written to the error log.This option may be given multiple times. Values that begin with
+or-are added to or subtracted from the previous value. For example,--debug=T--debug=+Psets the value toP:T.For more information, see Section 26.5.3, “The DBUG Package”.
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Command-Line Format --debug-sync-timeout[=#]Permitted Values Type integerControls whether the Debug Sync facility for testing and debugging is enabled. Use of Debug Sync requires that MySQL be configured with the
-DENABLE_DEBUG_SYNC=1CMake option (see Section 2.9.4, “MySQL Source-Configuration Options”). If Debug Sync is not compiled in, this option is not available. The option value is a timeout in seconds. The default value is 0, which disables Debug Sync. To enable it, specify a value greater than 0; this value also becomes the default timeout for individual synchronization points. If the option is given without a value, the timeout is set to 300 seconds.For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.
--default-authentication-plugin=plugin_nameRemoved 5.7.2 Command-Line Format --default-authentication-plugin=plugin_namePermitted Values Type enumerationDefault mysql_native_passwordValid Values mysql_native_passwordsha256_passwordThis option sets the default authentication plugin. It was removed in MySQL 5.7.2 and replaced by the
default_authentication_pluginsystem variable. The variable is used the same way as the option at server startup, but also enables the default plugin value to be inspected as runtime. For usage details, see the description ofdefault_authentication_plugin.-
Command-Line Format --default-storage-engine=nameSystem Variable Name default_storage_engineVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type enumerationDefault InnoDBSet the default storage engine for tables. See Chapter 16, Alternative Storage Engines. This option sets the storage engine for permanent tables only. To set the storage engine for
TEMPORARYtables, set thedefault_tmp_storage_enginesystem variable.If you disable the default storage engine at server startup, you must set the default engine for both permanent and
TEMPORARYtables to a different engine or the server will not start. -
Command-Line Format --default-time-zone=namePermitted Values Type stringSet the default server time zone. This option sets the global
time_zonesystem variable. If this option is not given, the default time zone is the same as the system time zone (given by the value of thesystem_time_zonesystem variable. --defaults-extra-file=file_nameRead this option file after the global option file but (on Unix) before the user option file. If the file does not exist or is otherwise inaccessible, an error occurs.
file_nameis interpreted relative to the current directory if given as a relative path name rather than a full path name.Use only the given option file. If the file does not exist or is otherwise inaccessible, an error occurs.
file_nameis interpreted relative to the current directory if given as a relative path name rather than a full path name.Read not only the usual option groups, but also groups with the usual names and a suffix of
str. For example, mysqld normally reads the[mysqld]group. If the--defaults-group-suffix=_otheroption is given, mysqld also reads the[mysqld_other]group.--delay-key-write[={OFF|ON|ALL}]Command-Line Format --delay-key-write[=name]System Variable Name delay_key_writeVariable Scope Global Dynamic Variable Yes Permitted Values Type enumerationDefault ONValid Values ONOFFALLSpecify how to use delayed key writes. Delayed key writing causes key buffers not to be flushed between writes for
MyISAMtables.OFFdisables delayed key writes.ONenables delayed key writes for those tables that were created with theDELAY_KEY_WRITEoption.ALLdelays key writes for allMyISAMtables. See Section 9.12.2, “Tuning Server Parameters”, and Section 16.2.1, “MyISAM Startup Options”.NoteIf you set this variable to
ALL, you should not useMyISAMtables from within another program (such as another MySQL server or myisamchk) when the tables are in use. Doing so leads to index corruption.-
Command-Line Format --des-key-file=file_nameRead the default DES keys from this file. These keys are used by the
DES_ENCRYPT()andDES_DECRYPT()functions. --early-plugin-load=plugin_listIntroduced 5.7.11 Command-Line Format --early-plugin-load=plugin_listPermitted Values (5.7.11) Type stringDefault keyring_file plugin library file namePermitted Values (>= 5.7.12) Type stringDefault empty stringThis option tells the server which plugins to load before loading mandatory built-in plugins and before storage engine initialization. If multiple
--early-plugin-loadoptions are given, only the last one is used.The option value is a semicolon-separated list of
name=plugin_libraryandplugin_libraryvalues. Eachnameis the name of a plugin to load, andplugin_libraryis the name of the library file that contains the plugin code. If a plugin library is named without any preceding plugin name, the server loads all plugins in the library. The server looks for plugin library files in the directory named by theplugin_dirsystem variable.For example, if plugins named
myplug1andmyplug2have library filesmyplug1.soandmyplug2.so, use this option to perform an early plugin load:shell>
mysqld --early-plugin-load="myplug1=myplug1.so;myplug2=myplug2.so"Quotes are used around the argument value because otherwise a semicolon (
;) is interpreted as a special character by some command interpreters. (Unix shells treat it as a command terminator, for example.)Each named plugin is loaded early for a single invocation of mysqld only. After a restart, the plugin is not loaded early unless
--early-plugin-loadis used again.If the server is started using
--initializeor--initialize-insecure, plugins specified by--early-plugin-loadare not loaded.If the server is run with
--help, plugins specified by--early-plugin-loadare loaded but not initialized. This behavior ensures that plugin options are displayed in the help message.As of MySQL 5.7.12, the default
--early-plugin-loadvalue is empty. To load your chosen keyring plugin, you must use an explicit--early-plugin-loadoption with a nonempty value.ImportantIn MySQL 5.7.11, the default
--early-plugin-loadvalue was the name of thekeyring_fileplugin library file, so that plugin was loaded by default.InnoDBtablespace encryption requires thekeyring_fileplugin to be loaded prior toInnoDBinitialization, so this change of default--early-plugin-loadvalue introduces an incompatibility for upgrades from 5.7.11 to 5.7.12 or higher. Administrators who have encryptedInnoDBtablespaces must take explicit action to ensure continued loading of thekeyring_fileplugin: Start the server with an--early-plugin-loadoption that names the plugin library file. For additional information, see Section 7.5.3.1, “Keyring Plugin Installation”.The
InnoDBtablespace encryption feature relies on thekeyring_fileplugin for encryption key management, and thekeyring_fileplugin must be loaded prior to storage engine initialization to facilitateInnoDBrecovery for encrypted tables. In MySQL 5.7.11, if you do not want to load thekeyring_fileplugin at server startup, specify an empty string (--early-plugin-load="").For information about
InnoDBtablespace encryption, see Section 15.7.10, “InnoDB Tablespace Encryption”. For general information about plugin loading, see Section 6.5.2, “Installing and Uninstalling Plugins”.-
Command-Line Format --enable-named-pipePlatform Specific Windows Enable support for named pipes. This option applies only on Windows.
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Command-Line Format --event-scheduler[=value]System Variable Name event_schedulerVariable Scope Global Dynamic Variable Yes Permitted Values Type enumerationDefault OFFValid Values ONOFFDISABLEDEnable or disable, and start or stop, the event scheduler.
For detailed information, see The
--event-schedulerOption. --exit-info[=,flags]-T [flags]Command-Line Format --exit-info[=flags]Permitted Values Type integerThis is a bit mask of different flags that you can use for debugging the mysqld server. Do not use this option unless you know exactly what it does!
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Command-Line Format --external-lockingPermitted Values Type booleanDefault FALSEEnable external locking (system locking), which is disabled by default. If you use this option on a system on which
lockddoes not fully work (such as Linux), it is easy for mysqld to deadlock.To disable external locking explicitly, use
--skip-external-locking.External locking affects only
MyISAMtable access. For more information, including conditions under which it can and cannot be used, see Section 9.11.5, “External Locking”. -
Command-Line Format --flushSystem Variable Name flushVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFFlush (synchronize) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.5.3.3, “What to Do If MySQL Keeps Crashing”.
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Command-Line Format --gdbPermitted Values Type booleanDefault FALSEInstall an interrupt handler for
SIGINT(needed to stop mysqld with^Cto set breakpoints) and disable stack tracing and core file handling. See Section 26.5, “Debugging and Porting MySQL”. -
Command-Line Format --general-logSystem Variable Name general_logVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFSpecify the initial general query log state. With no argument or an argument of 1, the
--general-logoption enables the log. If omitted or given with an argument of 0, the option disables the log. -
Command-Line Format --ignore-db-dirPermitted Values Type directory nameThis option tells the server to ignore the given directory name for purposes of the
SHOW DATABASESstatement orINFORMATION_SCHEMAtables. For example, if a MySQL configuration locates the data directory at the root of a file system on Unix, the system might create alost+founddirectory there that the server should ignore. Starting the server with--ignore-db-dir=lost+foundcauses that name not to be listed as a database.To specify more than one name, use this option multiple times, once for each name. Specifying the option with an empty value (that is, as
--ignore-db-dir=) resets the directory list to the empty list.Instances of this option given at server startup are used to set the
ignore_db_dirssystem variable. -
Introduced 5.7.6 Command-Line Format --initializePermitted Values Type booleanDefault OFFThis option is used to initialize a MySQL installation by creating the data directory and populating the tables in the
mysqlsystem database. For more information, see Section 2.10.1.1, “Initializing the Data Directory Manually Using mysqld”.When the server is started with
--initialize, some functionality is unavailable that limits the statements permitted in any file named by the--init-fileoption. For more information, see the description of that option. In addition, thedisabled_storage_enginessystem variable has no effect.In MySQL 5.7.7 and earlier, global transaction identifiers (GTIDs) were automatically disabled whenever
--initializewas enabled. In MySQL 5.7.8 and later GTIDs are not disabled when--initializeis enabled.--initializeis mutually exclusive with--bootstrapand--daemonize. -
Introduced 5.7.6 Command-Line Format --initialize-insecurePermitted Values Type booleanDefault OFFThis option is used to initialize a MySQL installation by creating the data directory and populating the tables in the
mysqlsystem database. This option implies--initialize. For more information, see the description of that option, and Section 2.10.1.1, “Initializing the Data Directory Manually Using mysqld”.--initialize-insecureis mutually exclusive with--bootstrapand--daemonize. -
Command-Line Format --init-file=file_nameSystem Variable Name init_fileVariable Scope Global Dynamic Variable No Permitted Values Type file nameRead SQL statements from this file at startup. Each statement must be on a single line and should not include comments.
If the server is started with any of the
--bootstrap,--initialize, or--initialize-insecureoptions, it operates in bootstap mode and some functionality is unavailable that limits the statements permitted in the file. These include statements that relate to account management (such asCREATE USERorGRANT), replication, and global transaction identifiers. See Section 18.1.3, “Replication with Global Transaction Identifiers”. --innodb-xxxSet an option for the
InnoDBstorage engine. TheInnoDBoptions are listed in Section 15.14, “InnoDB Startup Options and System Variables”.-
Command-Line Format --install [service_name]Platform Specific Windows (Windows only) Install the server as a Windows service that starts automatically during Windows startup. The default service name is
MySQLif noservice_namevalue is given. For more information, see Section 2.3.5.8, “Starting MySQL as a Windows Service”.NoteIf the server is started with the
--defaults-fileand--installoptions,--installmust be first. --install-manual [service_name]Command-Line Format --install-manual [service_name]Platform Specific Windows (Windows only) Install the server as a Windows service that must be started manually. It does not start automatically during Windows startup. The default service name is
MySQLif noservice_namevalue is given. For more information, see Section 2.3.5.8, “Starting MySQL as a Windows Service”.NoteIf the server is started with the
--defaults-fileand--install-manualoptions,--install-manualmust be first.--language=lang_name, -Llang_nameDeprecated 5.6.1, by lc-messages-dir Command-Line Format --language=nameSystem Variable Name languageVariable Scope Global Dynamic Variable No Permitted Values Type directory nameDefault /usr/local/mysql/share/mysql/english/The language to use for error messages.
lang_namecan be given as the language name or as the full path name to the directory where the language files are installed. See Section 11.2, “Setting the Error Message Language”.--lc-messages-dirand--lc-messagesshould be used rather than--language, which is deprecated (and handled as an alias for--lc-messages-dir). The--languageoption will be removed in a future MySQL release.-
Command-Line Format --large-pagesSystem Variable Name large_pagesVariable Scope Global Dynamic Variable No Platform Specific Linux Permitted Values (Linux) Type booleanDefault FALSESome hardware/operating system architectures support memory pages greater than the default (usually 4KB). The actual implementation of this support depends on the underlying hardware and operating system. Applications that perform a lot of memory accesses may obtain performance improvements by using large pages due to reduced Translation Lookaside Buffer (TLB) misses.
MySQL supports the Linux implementation of large page support (which is called HugeTLB in Linux). See Section 9.12.5.2, “Enabling Large Page Support”. For Solaris support of large pages, see the description of the
--super-large-pagesoption.--large-pagesis disabled by default. -
Command-Line Format --lc-messages=nameSystem Variable Name lc_messagesVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringDefault en_USThe locale to use for error messages. The default is
en_US. The server converts the argument to a language name and combines it with the value of--lc-messages-dirto produce the location for the error message file. See Section 11.2, “Setting the Error Message Language”. -
Command-Line Format --lc-messages-dir=dir_nameSystem Variable Name lc_messages_dirVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe directory where error messages are located. The server uses the value together with the value of
--lc-messagesto produce the location for the error message file. See Section 11.2, “Setting the Error Message Language”. -
Command-Line Format --local-service(Windows only) A
--local-serviceoption following the service name causes the server to run using theLocalServiceWindows account that has limited system privileges. This account is available only for Windows XP or newer. If both--defaults-fileand--local-serviceare given following the service name, they can be in any order. See Section 2.3.5.8, “Starting MySQL as a Windows Service”. -
Command-Line Format --log-error[=file_name]System Variable Name log_errorVariable Scope Global Dynamic Variable No Permitted Values Type file nameLog errors and startup messages to this file. See Section 6.4.2, “The Error Log”. If you omit the file name, MySQL uses
host_name.err.err. -
Command-Line Format --log-isam[=file_name]Permitted Values Type file nameLog all
MyISAMchanges to this file (used only when debuggingMyISAM). -
Command-Line Format --log-output=nameSystem Variable Name log_outputVariable Scope Global Dynamic Variable Yes Permitted Values Type setDefault FILEValid Values TABLEFILENONEThis option determines the destination for general query log and slow query log output. The option value can be given as one or more of the words
TABLE,FILE, orNONE.TABLEselect logging to thegeneral_logandslow_logtables in themysqldatabase as a destination.FILEselects logging to log files as a destination.NONEdisables logging. IfNONEis present in the option value, it takes precedence over any other words that are present.TABLEandFILEcan both be given to select to both log output destinations.This option selects log output destinations, but does not enable log output. To do that, use the
--general_logand--slow_query_logoptions. ForFILElogging, the--general_log_fileand-slow_query_log_fileoptions determine the log file location. For more information, see Section 6.4.1, “Selecting General Query and Slow Query Log Output Destinations”. --log-queries-not-using-indexesCommand-Line Format --log-queries-not-using-indexesSystem Variable Name log_queries_not_using_indexesVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFIf you are using this option with the slow query log enabled, queries that are expected to retrieve all rows are logged. See Section 6.4.5, “The Slow Query Log”. This option does not necessarily mean that no index is used. For example, a query that uses a full index scan uses an index but would be logged because the index would not limit the number of rows.
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Command-Line Format --log-raw[=value]Permitted Values Type booleanDefault OFFPasswords in certain statements written to the general query log, slow query log, and binary log are rewritten by the server not to occur literally in plain text. Password rewriting can be suppressed for the general query log by starting the server with the
--log-rawoption. This option may be useful for diagnostic purposes, to see the exact text of statements as received by the server, but for security reasons is not recommended for production use.If a query rewrite plugin is installed, the
--log-rawoption affects statement logging as follows:For more information, see Section 7.1.2.3, “Passwords and Logging”.
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Command-Line Format --log-short-formatPermitted Values Type booleanDefault FALSELog less information to the slow query log, if it has been activated.
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Removed 5.7.1 Command-Line Format --log-slow-admin-statements(5.7.0)Permitted Values Type booleanDefault OFFInclude slow administrative statements in the statements written to the slow query log. Administrative statements include
ALTER TABLE,ANALYZE TABLE,CHECK TABLE,CREATE INDEX,DROP INDEX,OPTIMIZE TABLE, andREPAIR TABLE.This command-line option was removed in MySQL 5.7.1 and replaced by the
log_slow_admin_statementssystem variable. The system variable can be set on the command line or in option files the same way as the option, so there is no need for any changes at server startup, but the system variable also makes it possible to examine or set the value at runtime. -
Command-Line Format --log-tc=file_namePermitted Values Type file nameDefault tc.logThe name of the memory-mapped transaction coordinator log file (for XA transactions that affect multiple storage engines when the binary log is disabled). The default name is
tc.log. The file is created under the data directory if not given as a full path name. This option is unused. -
Command-Line Format --log-tc-size=#Permitted Values (32-bit platforms) Type integerDefault 24576Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 24576Max Value 18446744073709551615The size in bytes of the memory-mapped transaction coordinator log. The default size is 24KB.
--log-warnings[=,level]-W [level]Deprecated 5.7.2 Command-Line Format --log-warnings[=#]System Variable Name log_warningsVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms, <= 5.7.1) Type integerDefault 1Min Value 0Max Value 4294967295Permitted Values (32-bit platforms, >= 5.7.2) Type integerDefault 2Min Value 0Max Value 4294967295Permitted Values (64-bit platforms, <= 5.7.1) Type integerDefault 1Min Value 0Max Value 18446744073709551615Permitted Values (64-bit platforms, >= 5.7.2) Type integerDefault 2Min Value 0Max Value 18446744073709551615NoteAs of MySQL 5.7.2, the
log_error_verbositysystem variable is preferred over, and should be used instead of, the--log-warningsoption orlog_warningssystem variable. For more information, see the descriptions oflog_error_verbosityandlog_warnings. The--log-warningscommand-line option andlog_warningssystem variable are deprecated and will be removed in a future MySQL release.Whether to produce additional warning messages to the error log. This option is enabled by default (the default is 1 before MySQL 5.7.2, 2 as of 5.7.2). To disable it, use
--log-warnings=0. Specifying the option without alevelvalue increments the current value by 1. The server logs messages about statements that are unsafe for statement-based logging if the value is greater than 0. Aborted connections and access-denied errors for new connection attempts are logged if the value is greater than 1. See Section B.5.2.11, “Communication Errors and Aborted Connections”.-
Command-Line Format --low-priority-updatesSystem Variable Name low_priority_updatesVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault FALSEGive table-modifying operations (
INSERT,REPLACE,DELETE,UPDATE) lower priority than selects. This can also be done using{INSERT | REPLACE | DELETE | UPDATE} LOW_PRIORITY ...to lower the priority of only one query, or bySET LOW_PRIORITY_UPDATES=1to change the priority in one thread. This affects only storage engines that use only table-level locking (MyISAM,MEMORY,MERGE). See Section 9.11.2, “Table Locking Issues”. --min-examined-row-limit=numberCommand-Line Format --min-examined-row-limit=#System Variable Name min_examined_row_limitVariable Scope Global, Session Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 0Min Value 0Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 0Min Value 0Max Value 18446744073709551615When this option is set, queries which examine fewer than
numberrows are not written to the slow query log. The default is 0.-
Command-Line Format --memlockPermitted Values Type booleanDefault FALSELock the mysqld process in memory. This option might help if you have a problem where the operating system is causing mysqld to swap to disk.
--memlockworks on systems that support themlockall()system call; this includes Solaris, most Linux distributions that use a 2.4 or higher kernel, and perhaps other Unix systems. On Linux systems, you can tell whether or notmlockall()(and thus this option) is supported by checking to see whether or not it is defined in the systemmman.hfile, like this:shell>
grep mlockall /usr/include/sys/mman.hIf
mlockall()is supported, you should see in the output of the previous command something like the following:extern int mlockall (int __flags) __THROW;
ImportantUse of this option may require you to run the server as
root, which, for reasons of security, is normally not a good idea. See Section 7.1.5, “How to Run MySQL as a Normal User”.On Linux and perhaps other systems, you can avoid the need to run the server as
rootby changing thelimits.conffile. See the notes regarding the memlock limit in Section 9.12.5.2, “Enabling Large Page Support”.You must not try to use this option on a system that does not support the
mlockall()system call; if you do so, mysqld will very likely crash as soon as you try to start it. -
Command-Line Format --myisam-block-size=#Permitted Values Type integerDefault 1024Min Value 1024Max Value 16384The block size to be used for
MyISAMindex pages. --myisam-recover-options[=option[,option]...]]Command-Line Format --myisam-recover-options[=name]Permitted Values Type enumerationDefault OFFValid Values OFFDEFAULTBACKUPFORCEQUICKSet the
MyISAMstorage engine recovery mode. The option value is any combination of the values ofOFF,DEFAULT,BACKUP,FORCE, orQUICK. If you specify multiple values, separate them by commas. Specifying the option with no argument is the same as specifyingDEFAULT, and specifying with an explicit value of""disables recovery (same as a value ofOFF). If recovery is enabled, each time mysqld opens aMyISAMtable, it checks whether the table is marked as crashed or was not closed properly. (The last option works only if you are running with external locking disabled.) If this is the case, mysqld runs a check on the table. If the table was corrupted, mysqld attempts to repair it.The following options affect how the repair works.
Option Description OFFNo recovery. DEFAULTRecovery without backup, forcing, or quick checking. BACKUPIf the data file was changed during recovery, save a backup of the tbl_name.MYDtbl_name-datetime.BAKFORCERun recovery even if we would lose more than one row from the .MYDfile.QUICKDo not check the rows in the table if there are not any delete blocks. Before the server automatically repairs a table, it writes a note about the repair to the error log. If you want to be able to recover from most problems without user intervention, you should use the options
BACKUP,FORCE. This forces a repair of a table even if some rows would be deleted, but it keeps the old data file as a backup so that you can later examine what happened.Do not read any option files. If program startup fails due to reading unknown options from an option file,
--no-defaultscan be used to prevent them from being read.The exception is that the
.mylogin.cnffile, if it exists, is read in all cases. This permits passwords to be specified in a safer way than on the command line even when--no-defaultsis used. (.mylogin.cnfis created by the mysql_config_editor utility. See Section 5.6.6, “mysql_config_editor — MySQL Configuration Utility”.)-
Command-Line Format --old-alter-tableSystem Variable Name old_alter_tableVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault OFFWhen this option is given, the server does not use the optimized method of processing an
ALTER TABLEoperation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation ofALTER TABLE, see Section 14.1.8, “ALTER TABLE Syntax”. -
Command-Line Format --old-style-user-limitsPermitted Values Type booleanDefault FALSEEnable old-style user limits. (Before MySQL 5.0.3, account resource limits were counted separately for each host from which a user connected rather than per account row in the
usertable.) See Section 7.3.4, “Setting Account Resource Limits”. -
Command-Line Format --open-files-limit=#System Variable Name open_files_limitVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 5000, with possible adjustmentMin Value 0Max Value platform dependentChanges the number of file descriptors available to mysqld. You should try increasing the value of this option if mysqld gives you the error
Too many open files. mysqld uses the option value to reserve descriptors withsetrlimit(). Internally, the maximum value for this option is the maximum unsigned integer value, but the actual maximum is platform dependent. If the requested number of file descriptors cannot be allocated, mysqld writes a warning to the error log.mysqld may attempt to allocate more than the requested number of descriptors (if they are available), using the values of
max_connectionsandtable_open_cacheto estimate whether more descriptors will be needed.On Unix, the value cannot be set less than ulimit -n.
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Deprecated 5.7.16 Command-Line Format --partitionDisabled by skip-partitionPermitted Values Type booleanDefault ONEnables or disables user-defined partitioning support in the MySQL Server.
This option is deprecated in MySQL 5.7.16, and is removed from MySQL 8.0.
--performance-schema-xxxConfigure a Performance Schema option. For details, see Section 23.11, “Performance Schema Command Options”.
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Command-Line Format --pid-file=file_nameSystem Variable Name pid_fileVariable Scope Global Dynamic Variable No Permitted Values Type file nameThe path name of the process ID file. The server creates the file in the data directory unless an absolute path name is given to specify a different directory. This file is used by other programs such as mysqld_safe to determine the server's process ID.
Specifies an option that pertains to a server plugin. For example, many storage engines can be built as plugins, and for such engines, options for them can be specified with a
--pluginprefix. Thus, the--innodb_file_per_tableoption forInnoDBcan be specified as--plugin-innodb_file_per_table.For boolean options that can be enabled or disabled, the
--skipprefix and other alternative formats are supported as well (see Section 5.2.5, “Program Option Modifiers”). For example,--skip-plugin-innodb_file_per_tabledisablesinnodb_file_per_table.The rationale for the
--pluginprefix is that it enables plugin options to be specified unambiguously if there is a name conflict with a built-in server option. For example, were a plugin writer to name a plugin “sql” and implement a “mode” option, the option name might be--sql-mode, which would conflict with the built-in option of the same name. In such cases, references to the conflicting name are resolved in favor of the built-in option. To avoid the ambiguity, users can specify the plugin option as--plugin-sql-mode. Use of the--pluginprefix for plugin options is recommended to avoid any question of ambiguity.-
Command-Line Format --plugin-load=plugin_listPermitted Values Type stringThis option tells the server to load the named plugins at startup. If multiple
--plugin-loadoptions are given, only the last one is used. Additional plugins to load may be specified using--plugin-load-addoptions.The option value is a semicolon-separated list of
name=plugin_libraryandplugin_libraryvalues. Eachnameis the name of a plugin to load, andplugin_libraryis the name of the library file that contains the plugin code. If a plugin library is named without any preceding plugin name, the server loads all plugins in the library. The server looks for plugin library files in the directory named by theplugin_dirsystem variable.For example, if plugins named
myplug1andmyplug2have library filesmyplug1.soandmyplug2.so, use this option to perform an early plugin load:shell>
mysqld --plugin-load="myplug1=myplug1.so;myplug2=myplug2.so"Quotes are used around the argument value here because otherwise semicolon (
;) is interpreted as a special character by some command interpreters. (Unix shells treat it as a command terminator, for example.)Each named plugin is loaded for a single invocation of mysqld only. After a restart, the plugin is not loaded unless
--plugin-loadis used again. This is in contrast toINSTALL PLUGIN, which adds an entry to themysql.pluginstable to cause the plugin to be loaded for every normal server startup.Under normal startup, the server determines which plugins to load by reading the
mysql.pluginssystem table. If the server is started with the--skip-grant-tablesoption, it does not consult themysql.pluginstable and does not load plugins listed there.--plugin-loadenables plugins to be loaded even when--skip-grant-tablesis given.--plugin-loadalso enables plugins to be loaded at startup that cannot be loaded at runtime.For additional information about plugin loading, see Section 6.5.2, “Installing and Uninstalling Plugins”.
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Command-Line Format --plugin-load-add=plugin_listPermitted Values Type stringThis option complements the
--plugin-loadoption.--plugin-load-addadds a plugin or plugins to the set of plugins to be loaded at startup. The argument format is the same as for--plugin-load.--plugin-load-addcan be used to avoid specifying a large set of plugins as a single long unwieldy--plugin-loadargument.--plugin-load-addcan be given in the absence of--plugin-load, but any instance of--plugin-load-addthat appears before--plugin-load. has no effect because--plugin-loadresets the set of plugins to load. In other words, these options:--plugin-load=x --plugin-load-add=y
are equivalent to this option:
--plugin-load="x;y"
But these options:
--plugin-load-add=y --plugin-load=x
are equivalent to this option:
--plugin-load=x
For additional information about plugin loading, see Section 6.5.2, “Installing and Uninstalling Plugins”.
--port=,port_num-Pport_numCommand-Line Format --port=#System Variable Name portVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 3306Min Value 0Max Value 65535The port number to use when listening for TCP/IP connections. On Unix and Unix-like systems, the port number must be 1024 or higher unless the server is started by the
rootsystem user.-
Command-Line Format --port-open-timeout=#Permitted Values Type integerDefault 0On some systems, when the server is stopped, the TCP/IP port might not become available immediately. If the server is restarted quickly afterward, its attempt to reopen the port can fail. This option indicates how many seconds the server should wait for the TCP/IP port to become free if it cannot be opened. The default is not to wait.
Print the program name and all options that it gets from option files.
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Command-Line Format --remove [service_name]Platform Specific Windows (Windows only) Remove a MySQL Windows service. The default service name is
MySQLif noservice_namevalue is given. For more information, see Section 2.3.5.8, “Starting MySQL as a Windows Service”. -
Command-Line Format --safe-user-createPermitted Values Type booleanDefault FALSEIf this option is enabled, a user cannot create new MySQL users by using the
GRANTstatement unless the user has theINSERTprivilege for themysql.usertable or any column in the table. If you want a user to have the ability to create new users that have those privileges that the user has the right to grant, you should grant the user the following privilege:GRANT INSERT(user) ON mysql.user TO '
user_name'@'host_name';This ensures that the user cannot change any privilege columns directly, but has to use the
GRANTstatement to give privileges to other users. -
Deprecated 5.7.5 Command-Line Format --secure-authSystem Variable Name secure_authVariable Scope Global Dynamic Variable Yes Permitted Values (<= 5.7.4) Type booleanDefault ONValid Values OFFONPermitted Values (>= 5.7.5) Type booleanDefault ONValid Values ONThis option causes the server to block connections by clients that attempt to use accounts that have passwords stored in the old (pre-4.1) format. Use it to prevent all use of passwords employing the old format (and hence insecure communication over the network).
As of MySQL 5.7.5, this option is deprecated and will be removed in a future MySQL release. It is always enabled and attempting to disable it (
--skip-secure-auth,--secure-auth=0) produces an error. Before MySQL 5.7.5, this option is enabled by default but can be disabled.Server startup fails with an error if this option is enabled and the privilege tables are in pre-4.1 format. See Section B.5.2.4, “Client does not support authentication protocol”.
The mysql client also has a
--secure-authoption, which prevents connections to a server if the server requires a password in old format for the client account.NotePasswords that use the pre-4.1 hashing method are less secure than passwords that use the native password hashing method and should be avoided. Pre-4.1 passwords are deprecated and support for them is removed in MySQL 5.7.5. For account upgrade instructions, see Section 7.5.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.
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Command-Line Format --secure-file-priv=dir_nameSystem Variable Name secure_file_privVariable Scope Global Dynamic Variable No Permitted Values (<= 5.7.5) Type stringDefault emptyValid Values emptydirnamePermitted Values (>= 5.7.6) Type stringDefault platform specificValid Values emptydirnameNULLThis option sets the
secure_file_privsystem variable, which is used to limit the effect of data import and export operations, such as those performed by theLOAD DATAandSELECT ... INTO OUTFILEstatements and theLOAD_FILE()function. For more information, see the description ofsecure_file_priv. -
Command-Line Format --shared_memory[={0,1}]System Variable Name shared_memoryVariable Scope Global Dynamic Variable No Platform Specific Windows Permitted Values Type booleanDefault FALSEEnable shared-memory connections by local clients. This option is available only on Windows.
--shared-memory-base-name=nameCommand-Line Format --shared_memory_base_name=nameSystem Variable Name shared_memory_base_nameVariable Scope Global Dynamic Variable No Platform Specific Windows Permitted Values Type stringDefault MYSQLThe name of shared memory to use for shared-memory connections. This option is available only on Windows. The default name is
MYSQL. The name is case sensitive.Turn off the ability to select and insert at the same time on
MyISAMtables. (This is to be used only if you think you have found a bug in this feature.) See Section 9.11.3, “Concurrent Inserts”.-
Command-Line Format --skip-event-scheduler--disable-event-schedulerTurns the Event Scheduler
OFF. This is not the same as disabling the Event Scheduler, which requires setting--event-scheduler=DISABLED; see The--event-schedulerOption, for more information. This option causes the server to start without using the privilege system at all, which gives anyone with access to the server unrestricted access to all databases. You can cause a running server to start using the grant tables again by executing mysqladmin flush-privileges or mysqladmin reload command from a system shell, or by issuing a MySQL
FLUSH PRIVILEGESstatement after connecting to the server.This option also causes the server to suppress during its startup sequence the loading of user-defined functions (UDFs), scheduled events, and plugins that were installed with the
INSTALL PLUGINstatement. To cause plugins to be loaded anyway, use the--plugin-loadoption.--skip-grant-tablesalso causes thedisabled_storage_enginessystem variable to have no effect.FLUSH PRIVILEGESmight be executed implicitly by other actions performed after startup. For example, mysql_upgrade flushes the privileges during the upgrade procedure.Disable use of the internal host cache for faster name-to-IP resolution. In this case, the server performs a DNS lookup every time a client connects. See Section 9.12.6.2, “DNS Lookup Optimization and the Host Cache”.
Use of
--skip-host-cacheis similar to setting thehost_cache_sizesystem variable to 0, buthost_cache_sizeis more flexible because it can also be used to resize, enable, or disable the host cache at runtime, not just at server startup.If you start the server with
--skip-host-cache, that does not prevent changes to the value ofhost_cache_size, but such changes have no effect and the cache is not re-enabled even ifhost_cache_sizeis set larger than 0.Disable the
InnoDBstorage engine. In this case, because the default storage engine isInnoDB, the server will not start unless you also use--default-storage-engineand--default-tmp-storage-engineto set the default to some other engine for both permanent andTEMPORARYtables.As of MySQL 5.7.5, the
InnoDBstorage engine can no longer be disabled, and the--skip-innodboption is deprecated and has no effect. Its use results in a warning. This option will be removed in a future MySQL release.Do not resolve host names when checking client connections. Use only IP addresses. If you use this option, all
Hostcolumn values in the grant tables must be IP addresses. See Section 9.12.6.2, “DNS Lookup Optimization and the Host Cache”.Depending on the network configuration of your system and the
Hostvalues for your accounts, clients may need to connect using an explicit--hostoption, such as--host=127.0.0.1or--host=::1.An attempt to connect to the host
127.0.0.1normally resolves to thelocalhostaccount. However, this fails if the server is run with the--skip-name-resolveoption, so make sure that an account exists that can accept a connection. For example, to be able to connect asrootusing--host=127.0.0.1or--host=::1, create these accounts:CREATE USER 'root'@'127.0.0.1' IDENTIFIED BY '
root-password'; CREATE USER 'root'@'::1' IDENTIFIED BY 'root-password';Do not listen for TCP/IP connections at all. All interaction with mysqld must be made using named pipes or shared memory (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are permitted. See Section 9.12.6.2, “DNS Lookup Optimization and the Host Cache”.
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Deprecated 5.7.16 Command-Line Format --skip-partition--disable-partitionDisables user-defined partitioning. Partitioned tables can be seen using
SHOW TABLESor by querying theINFORMATION_SCHEMA.TABLEStable, but cannot be created or modified, nor can data in such tables be accessed. All partition-specific columns in theINFORMATION_SCHEMA.PARTITIONStable displayNULL.Since
DROP TABLEremoves table definition (.frm) files, this statement works on partitioned tables even when partitioning is disabled using the option. The statement, however, does not remove partition definitions associated with partitioned tables in such cases. For this reason, you should avoid dropping partitioned tables with partitioning disabled, or take action to remove orphaned.parfiles manually (if present).NoteAs of MySQL 5.7.6, partition definition (
.par) files are no longer created. Instead, partition definitions are stored in the internal data dictionary.This option is deprecated in MySQL 5.7.16, and is removed from MySQL 8.0.
Options that begin with
--sslspecify whether to permit clients to connect using SSL and indicate where to find SSL keys and certificates. See Section 7.4.5, “Command Options for Secure Connections”.-
Command-Line Format --standalonePlatform Specific Windows Available on Windows only; instructs the MySQL server not to run as a service.
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Command-Line Format --super-large-pagesPlatform Specific Solaris Permitted Values (Solaris) Type booleanDefault FALSEStandard use of large pages in MySQL attempts to use the largest size supported, up to 4MB. Under Solaris, a “super large pages” feature enables uses of pages up to 256MB. This feature is available for recent SPARC platforms. It can be enabled or disabled by using the
--super-large-pagesor--skip-super-large-pagesoption. --symbolic-links,--skip-symbolic-linksCommand-Line Format --symbolic-linksEnable or disable symbolic link support. On Unix, enabling symbolic links means that you can link a
MyISAMindex file or data file to another directory with theINDEX DIRECTORYorDATA DIRECTORYoptions of theCREATE TABLEstatement. If you delete or rename the table, the files that its symbolic links point to also are deleted or renamed. See Section 9.12.4.2, “Using Symbolic Links for MyISAM Tables on Unix”.This option has no meaning on Windows.
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Command-Line Format --skip-show-databaseSystem Variable Name skip_show_databaseVariable Scope Global Dynamic Variable No This option sets the
skip_show_databasesystem variable that controls who is permitted to use theSHOW DATABASESstatement. See Section 6.1.4, “Server System Variables”. -
Command-Line Format --skip-stack-traceDo not write stack traces. This option is useful when you are running mysqld under a debugger. On some systems, you also must use this option to get a core file. See Section 26.5, “Debugging and Porting MySQL”.
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Command-Line Format --slow-query-logSystem Variable Name slow_query_logVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFSpecify the initial slow query log state. With no argument or an argument of 1, the
--slow-query-logoption enables the log. If omitted or given with an argument of 0, the option disables the log. -
Command-Line Format --slow-start-timeout=#Permitted Values (Windows) Type integerDefault 15000This option controls the Windows service control manager's service start timeout. The value is the maximum number of milliseconds that the service control manager waits before trying to kill the windows service during startup. The default value is 15000 (15 seconds). If the MySQL service takes too long to start, you may need to increase this value. A value of 0 means there is no timeout.
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Command-Line Format --socket={file_name|pipe_name}System Variable Name socketVariable Scope Global Dynamic Variable No Permitted Values Type stringDefault /tmp/mysql.sockOn Unix, this option specifies the Unix socket file to use when listening for local connections. The default value is
/tmp/mysql.sock. If this option is given, the server creates the file in the data directory unless an absolute path name is given to specify a different directory. On Windows, the option specifies the pipe name to use when listening for local connections that use a named pipe. The default value isMySQL(not case sensitive). --sql-mode=value[,value[,value...]]Command-Line Format --sql-mode=nameSystem Variable Name sql_modeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (<= 5.7.4) Type setDefault NO_ENGINE_SUBSTITUTIONValid Values ALLOW_INVALID_DATESANSI_QUOTESERROR_FOR_DIVISION_BY_ZEROHIGH_NOT_PRECEDENCEIGNORE_SPACENO_AUTO_CREATE_USERNO_AUTO_VALUE_ON_ZERONO_BACKSLASH_ESCAPESNO_DIR_IN_CREATENO_ENGINE_SUBSTITUTIONNO_FIELD_OPTIONSNO_KEY_OPTIONSNO_TABLE_OPTIONSNO_UNSIGNED_SUBTRACTIONNO_ZERO_DATENO_ZERO_IN_DATEONLY_FULL_GROUP_BYPAD_CHAR_TO_FULL_LENGTHPIPES_AS_CONCATREAL_AS_FLOATSTRICT_ALL_TABLESSTRICT_TRANS_TABLESPermitted Values (>= 5.7.5, <= 5.7.6) Type setDefault ONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ENGINE_SUBSTITUTIONValid Values ALLOW_INVALID_DATESANSI_QUOTESERROR_FOR_DIVISION_BY_ZEROHIGH_NOT_PRECEDENCEIGNORE_SPACENO_AUTO_CREATE_USERNO_AUTO_VALUE_ON_ZERONO_BACKSLASH_ESCAPESNO_DIR_IN_CREATENO_ENGINE_SUBSTITUTIONNO_FIELD_OPTIONSNO_KEY_OPTIONSNO_TABLE_OPTIONSNO_UNSIGNED_SUBTRACTIONNO_ZERO_DATENO_ZERO_IN_DATEONLY_FULL_GROUP_BYPAD_CHAR_TO_FULL_LENGTHPIPES_AS_CONCATREAL_AS_FLOATSTRICT_ALL_TABLESSTRICT_TRANS_TABLESPermitted Values (5.7.7) Type setDefault ONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_AUTO_CREATE_USER NO_ENGINE_SUBSTITUTIONValid Values ALLOW_INVALID_DATESANSI_QUOTESERROR_FOR_DIVISION_BY_ZEROHIGH_NOT_PRECEDENCEIGNORE_SPACENO_AUTO_CREATE_USERNO_AUTO_VALUE_ON_ZERONO_BACKSLASH_ESCAPESNO_DIR_IN_CREATENO_ENGINE_SUBSTITUTIONNO_FIELD_OPTIONSNO_KEY_OPTIONSNO_TABLE_OPTIONSNO_UNSIGNED_SUBTRACTIONNO_ZERO_DATENO_ZERO_IN_DATEONLY_FULL_GROUP_BYPAD_CHAR_TO_FULL_LENGTHPIPES_AS_CONCATREAL_AS_FLOATSTRICT_ALL_TABLESSTRICT_TRANS_TABLESPermitted Values (>= 5.7.8) Type setDefault ONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ZERO_IN_DATE NO_ZERO_DATE ERROR_FOR_DIVISION_BY_ZERO NO_AUTO_CREATE_USER NO_ENGINE_SUBSTITUTIONValid Values ALLOW_INVALID_DATESANSI_QUOTESERROR_FOR_DIVISION_BY_ZEROHIGH_NOT_PRECEDENCEIGNORE_SPACENO_AUTO_CREATE_USERNO_AUTO_VALUE_ON_ZERONO_BACKSLASH_ESCAPESNO_DIR_IN_CREATENO_ENGINE_SUBSTITUTIONNO_FIELD_OPTIONSNO_KEY_OPTIONSNO_TABLE_OPTIONSNO_UNSIGNED_SUBTRACTIONNO_ZERO_DATENO_ZERO_IN_DATEONLY_FULL_GROUP_BYPAD_CHAR_TO_FULL_LENGTHPIPES_AS_CONCATREAL_AS_FLOATSTRICT_ALL_TABLESSTRICT_TRANS_TABLESSet the SQL mode. See Section 6.1.7, “Server SQL Modes”.
NoteMySQL installation programs may configure the SQL mode during the installation process. For example, mysql_install_db creates a default option file named
my.cnfin the base installation directory. This file contains a line that sets the SQL mode; see Section 5.4.2, “mysql_install_db — Initialize MySQL Data Directory”.If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.
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Command-Line Format --sysdate-is-nowPermitted Values Type booleanDefault FALSESYSDATE()by default returns the time at which it executes, not the time at which the statement in which it occurs begins executing. This differs from the behavior ofNOW(). This option causesSYSDATE()to be an alias forNOW(). For information about the implications for binary logging and replication, see the description forSYSDATE()in Section 13.7, “Date and Time Functions” and forSET TIMESTAMPin Section 6.1.4, “Server System Variables”. --tc-heuristic-recover={COMMIT|ROLLBACK}Command-Line Format --tc-heuristic-recover=namePermitted Values Type enumerationDefault COMMITValid Values COMMITROLLBACKThe type of decision to use in the heuristic recovery process. This option is unused.
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Command-Line Format --temp-poolPermitted Values Type booleanDefault TRUEThis option causes most temporary files created by the server to use a small set of names, rather than a unique name for each new file. This works around a problem in the Linux kernel dealing with creating many new files with different names. With the old behavior, Linux seems to “leak” memory, because it is being allocated to the directory entry cache rather than to the disk cache. This option is ignored except on Linux.
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Command-Line Format --transaction-isolation=namePermitted Values Type enumerationDefault REPEATABLE-READValid Values READ-UNCOMMITTEDREAD-COMMITTEDREPEATABLE-READSERIALIZABLESets the default transaction isolation level. The
levelvalue can beREAD-UNCOMMITTED,READ-COMMITTED,REPEATABLE-READ, orSERIALIZABLE. See Section 14.3.6, “SET TRANSACTION Syntax”.The default transaction isolation level can also be set at runtime using the
SET TRANSACTIONstatement or by setting thetx_isolationsystem variable. -
Command-Line Format --transaction-read-onlyPermitted Values Type booleanDefault OFFSets the default transaction access mode. By default, read-only mode is disabled, so the mode is read/write.
To set the default transaction access mode at runtime, use the
SET TRANSACTIONstatement or set thetx_read_onlysystem variable. See Section 14.3.6, “SET TRANSACTION Syntax”. --tmpdir=,dir_name-tdir_nameCommand-Line Format --tmpdir=dir_nameSystem Variable Name tmpdirVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe path of the directory to use for creating temporary files. It might be useful if your default
/tmpdirectory resides on a partition that is too small to hold temporary tables. This option accepts several paths that are used in round-robin fashion. Paths should be separated by colon characters (“:”) on Unix and semicolon characters (“;”) on Windows. If the MySQL server is acting as a replication slave, you should not set--tmpdirto point to a directory on a memory-based file system or to a directory that is cleared when the server host restarts. For more information about the storage location of temporary files, see Section B.5.3.5, “Where MySQL Stores Temporary Files”. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables orLOAD DATA INFILEoperations. If files in the temporary file directory are lost when the server restarts, replication fails.--user={,user_name|user_id}-u {user_name|user_id}Command-Line Format --user=namePermitted Values Type stringRun the mysqld server as the user having the name
user_nameor the numeric user IDuser_id. (“User” in this context refers to a system login account, not a MySQL user listed in the grant tables.)This option is mandatory when starting mysqld as
root. The server changes its user ID during its startup sequence, causing it to run as that particular user rather than asroot. See Section 7.1.1, “Security Guidelines”.To avoid a possible security hole where a user adds a
--user=rootoption to amy.cnffile (thus causing the server to run asroot), mysqld uses only the first--useroption specified and produces a warning if there are multiple--useroptions. Options in/etc/my.cnfand$MYSQL_HOME/my.cnfare processed before command-line options, so it is recommended that you put a--useroption in/etc/my.cnfand specify a value other thanroot. The option in/etc/my.cnfis found before any other--useroptions, which ensures that the server runs as a user other thanroot, and that a warning results if any other--useroption is found.Use this option with the
--helpoption for detailed help.--version,-VDisplay version information and exit.
The MySQL server maintains many system variables that indicate how
it is configured. Each system variable has a default value. System
variables can be set at server startup using options on the
command line or in an option file. Most of them can be changed
dynamically while the server is running by means of the
SET
statement, which enables you to modify operation of the server
without having to stop and restart it. You can refer to system
variable values in expressions.
There are several ways to see the names and values of system variables:
To see the values that a server will use based on its compiled-in defaults and any option files that it reads, use this command:
mysqld --verbose --help
To see the values that a server will use based on its compiled-in defaults, ignoring the settings in any option files, use this command:
mysqld --no-defaults --verbose --help
To see the current values used by a running server, use the
SHOW VARIABLESstatement.
This section provides a description of each system variable. Variables with no version indicated are present in all MySQL 5.7 releases.
The following table lists all available system variables.
Table 6.2 System Variable Summary
For additional system variable information, see these sections:
Section 6.1.5, “Using System Variables”, discusses the syntax for setting and displaying system variable values.
Section 6.1.5.2, “Dynamic System Variables”, lists the variables that can be set at runtime.
Information on tuning system variables can be found in Section 9.12.2, “Tuning Server Parameters”.
Section 15.14, “InnoDB Startup Options and System Variables”, lists
InnoDBsystem variables.Section 19.3.3.8.2, “MySQL Cluster System Variables”, lists system variables which are specific to MySQL Cluster.
For information on server system variables specific to replication, see Section 18.1.6, “Replication and Binary Logging Options and Variables”.
Some of the following variable descriptions refer to
“enabling” or “disabling” a variable.
These variables can be enabled with the
SET
statement by setting them to ON or
1, or disabled by setting them to
OFF or 0. Boolean
variables can be set at startup to the values
ON, TRUE,
OFF, and FALSE (not case
sensitive), as well as 1 and
0. See Section 5.2.5, “Program Option Modifiers”.
Some system variables control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to a system variable that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server will adjust a value upward. For example, if you assign a value of 0 to a variable for which the minimal value is 1024, the server will set the value to 1024.
Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.
Some system variables take file name values. Unless otherwise
specified, the default file location is the data directory if the
value is a relative path name. To specify the location explicitly,
use an absolute path name. Suppose that the data directory is
/var/mysql/data. If a file-valued variable is
given as a relative path name, it will be located under
/var/mysql/data. If the value is an absolute
path name, its location is as given by the path name.
authentication_windows_log_levelIntroduced 5.7.9 Command-Line Format --authentication_windows_log_levelPermitted Values Type integerDefault 0Min Value 0Max Value 4This variable is available only if the
authentication_windowsWindows authentication plugin is enabled and debugging code is enabled. See Section 7.5.1.6, “The Windows Native Authentication Plugin”.This variable sets the logging level for the Windows authentication plugin. The following table shows the permitted values.
Value Description 0 No logging 1 Log only error messages 2 Log level 1 messages and warning messages 3 Log level 2 messages and information notes 4 Log level 3 messages and debug messages This variable was added in MySQL 5.7.9.
authentication_windows_use_principal_nameIntroduced 5.7.9 Command-Line Format --authentication_windows_use_principal_namePermitted Values Type booleanDefault ONThis variable is available only if the
authentication_windowsWindows authentication plugin is enabled. See Section 7.5.1.6, “The Windows Native Authentication Plugin”.A client that authenticates using the
InitSecurityContext()function should provide a string identifying the service to which it connects (targetName). MySQL uses the principal name (UPN) of the account under which the server is running. The UPN has the formuser_id@computer_nameThis variable controls whether the server sends the UPN in the initial challenge. By default, the variable is enabled. For security reasons, it can be disabled to avoid sending the server's account name to a client in clear text. If the variable is disabled, the server always sends a
0x00byte in the first challenge, the client does not specifytargetName, and as a result, NTLM authentication is used.If the server fails to obtain its UPN (which will happen primarily in environments that do not support Kerberos authentication), the UPN is not sent by the server and NTLM authentication is used.
This variable was added in MySQL 5.7.9.
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Command-Line Format --autocommit[=#]System Variable Name autocommitVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault ONThe autocommit mode. If set to 1, all changes to a table take effect immediately. If set to 0, you must use
COMMITto accept a transaction orROLLBACKto cancel it. Ifautocommitis 0 and you change it to 1, MySQL performs an automaticCOMMITof any open transaction. Another way to begin a transaction is to use aSTART TRANSACTIONorBEGINstatement. See Section 14.3.1, “START TRANSACTION, COMMIT, and ROLLBACK Syntax”.By default, client connections begin with
autocommitset to 1. To cause clients to begin with a default of 0, set the globalautocommitvalue by starting the server with the--autocommit=0option. To set the variable using an option file, include these lines:[mysqld] autocommit=0
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System Variable Name automatic_sp_privilegesVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault TRUEWhen this variable has a value of 1 (the default), the server automatically grants the
EXECUTEandALTER ROUTINEprivileges to the creator of a stored routine, if the user cannot already execute and alter or drop the routine. (TheALTER ROUTINEprivilege is required to drop the routine.) The server also automatically drops those privileges from the creator when the routine is dropped. Ifautomatic_sp_privilegesis 0, the server does not automatically add or drop these privileges.The creator of a routine is the account used to execute the
CREATEstatement for it. This might not be the same as the account named as theDEFINERin the routine definition.See also Section 21.2.2, “Stored Routines and MySQL Privileges”.
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Introduced 5.7.5 Command-Line Format --auto_generate_certs[={OFF|ON}]System Variable Name auto_generate_certsVariable Scope Global Dynamic Variable No Permitted Values Type booleanDefault ONThis variable is available if the server was compiled using OpenSSL (see Section 7.4.1, “OpenSSL Versus yaSSL”). It controls whether the server autogenerates SSL key and certificate files in the data directory, if they do not already exist.
At startup, the server automatically generates server-side and client-side SSL certificate and key files in the data directory if the
auto_generate_certssystem variable is enabled, no SSL options other than--sslare specified, and the server-side SSL files are missing from the data directory. These files enable secure client connections using SSL; see Section 7.4.4, “Configuring MySQL to Use Secure Connections”.For more information about SSL file autogeneration, including file names and characteristics, see Section 7.4.6.1, “Creating SSL and RSA Certificates and Keys using MySQL”
The
sha256_password_auto_generate_rsa_keyssystem variable is related but controls autogeneration of RSA key-pair files needed for secure password exchange using RSA over unencypted connections. -
Introduced 5.7.6 Deprecated 5.7.6 Command-Line Format --avoid_temporal_upgrade={OFF|ON}System Variable Name avoid_temporal_upgradeVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFThis variable controls whether
ALTER TABLEimplicitly upgrades temporal columns found to be in pre-5.6.4 format (TIME,DATETIME, andTIMESTAMPcolumns without support for fractional seconds precision). Upgrading such columns requires a table rebuild, which prevents any use of fast alterations that might otherwise apply to the operation to be performed.This variable is disabled by default. Enabling it causes
ALTER TABLEnot to rebuild temporal columns and thereby be able to take advantage of possible fast alterations.This variable is deprecated and will be removed in a future MySQL release.
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System Variable Name back_logVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault -1 (autosized)Min Value 1Max Value 65535The number of outstanding connection requests MySQL can have. This comes into play when the main MySQL thread gets very many connection requests in a very short time. It then takes some time (although very little) for the main thread to check the connection and start a new thread. The
back_logvalue indicates how many requests can be stacked during this short time before MySQL momentarily stops answering new requests. You need to increase this only if you expect a large number of connections in a short period of time.In other words, this value is the size of the listen queue for incoming TCP/IP connections. Your operating system has its own limit on the size of this queue. The manual page for the Unix
listen()system call should have more details. Check your OS documentation for the maximum value for this variable.back_logcannot be set higher than your operating system limit.The default value is based on the following formula, capped to a limit of 900:
50 + (max_connections / 5)
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Command-Line Format --basedir=dir_nameSystem Variable Name basedirVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe MySQL installation base directory. This variable can be set with the
--basediroption. Relative path names for other variables usually are resolved relative to the base directory. -
Command-Line Format --big-tablesSystem Variable Name big_tablesVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault OFFIf set to 1, all temporary tables are stored on disk rather than in memory. This is a little slower, but the error
The tabledoes not occur fortbl_nameis fullSELECToperations that require a large temporary table. The default value for a new connection is 0 (use in-memory temporary tables). Normally, you should never need to set this variable, because in-memory tables are automatically converted to disk-based tables as required. -
Command-Line Format --bind-address=addrSystem Variable Name bind_addressVariable Scope Global Dynamic Variable No Permitted Values Type stringDefault *The value of the
--bind-addressoption.This variable has no effect for the embedded server (
libmysqld) and as of MySQL 5.7.2 is no longer visible within the embedded server. -
Introduced 5.7.4 Command-Line Format --block_encryption_mode=#System Variable Name block_encryption_modeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringDefault aes-128-ecbThis variable controls the block encryption mode for block-based algorithms such as AES. It affects encryption for
AES_ENCRYPT()andAES_DECRYPT().block_encryption_modetakes a value inaes-format, wherekeylen-modekeylenis the key length in bits andmodeis the encryption mode. The value is not case sensitive. Permittedkeylenvalues are 128, 192, and 256. Permitted encryption modes depend on whether MySQL was compiled using OpenSSL or yaSSL:For OpenSSL, permitted
modevalues are:ECB,CBC,CFB1,CFB8,CFB128,OFBFor yaSSL, permitted
modevalues are:ECB,CBC
For example, this statement causes the AES encryption functions to use a key length of 256 bits and the CBC mode:
SET block_encryption_mode = 'aes-256-cbc';
An error occurs for attempts to set
block_encryption_modeto a value containing an unsupported key length or a mode that the SSL library does not support. -
Command-Line Format --bulk_insert_buffer_size=#System Variable Name bulk_insert_buffer_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 8388608Min Value 0Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 8388608Min Value 0Max Value 18446744073709551615MyISAMuses a special tree-like cache to make bulk inserts faster forINSERT ... SELECT,INSERT ... VALUES (...), (...), ..., andLOAD DATA INFILEwhen adding data to nonempty tables. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 disables this optimization. The default value is 8MB. -
System Variable Name character_set_clientVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringThe character set for statements that arrive from the client. The session value of this variable is set using the character set requested by the client when the client connects to the server. (Many clients support a
--default-character-setoption to enable this character set to be specified explicitly. See also Section 11.1.5, “Connection Character Sets and Collations”.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests:The client is from a version of MySQL older than MySQL 4.1, and thus does not request a character set.
The client requests a character set not known to the server. For example, a Japanese-enabled client requests
sjiswhen connecting to a server not configured withsjissupport.mysqld was started with the
--skip-character-set-client-handshakeoption, which causes it to ignore client character set configuration. This reproduces MySQL 4.0 behavior and is useful should you wish to upgrade the server without upgrading all the clients.
ucs2,utf16,utf16le, andutf32cannot be used as a client character set, which means that they also do not work forSET NAMESorSET CHARACTER SET. -
System Variable Name character_set_connectionVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringThe character set used for literals that do not have a character set introducer and for number-to-string conversion.
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System Variable Name character_set_databaseVariable Scope Global, Session Dynamic Variable Yes Footnote This option is dynamic, but only the server should set this information. You should not set the value of this variable manually. Permitted Values Type stringThe character set used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as
character_set_server.The global
character_set_databaseandcollation_databasesystem variables are deprecated as of MySQL 5.7.6 and will be removed in a future version of MySQL.Assigning a value to the session
character_set_databaseandcollation_databasesystem variables is deprecated as of MySQL 5.7.6 and assignments produce a warning. The session variables will become read only in a future version of MySQL and assignments will produce an error. It will remain possible to access the session variables to determine the database character set and collation for the default database. -
Command-Line Format --character-set-filesystem=nameSystem Variable Name character_set_filesystemVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringDefault binaryThe file system character set. This variable is used to interpret string literals that refer to file names, such as in the
LOAD DATA INFILEandSELECT ... INTO OUTFILEstatements and theLOAD_FILE()function. Such file names are converted fromcharacter_set_clienttocharacter_set_filesystembefore the file opening attempt occurs. The default value isbinary, which means that no conversion occurs. For systems on which multibyte file names are permitted, a different value may be more appropriate. For example, if the system represents file names using UTF-8, setcharacter_set_filesystemto'utf8'. -
System Variable Name character_set_resultsVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringThe character set used for returning query results such as result sets or error messages to the client.
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Command-Line Format --character-set-serverSystem Variable Name character_set_serverVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringDefault latin1The server's default character set.
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System Variable Name character_set_systemVariable Scope Global Dynamic Variable No Permitted Values Type stringDefault utf8The character set used by the server for storing identifiers. The value is always
utf8. -
Command-Line Format --character-sets-dir=dir_nameSystem Variable Name character_sets_dirVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe directory where character sets are installed.
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Introduced 5.7.7 Command-Line Format --check_proxy_users=[={OFF|ON}]System Variable Name check_proxy_usersVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFThis variable controls whether the server performs proxy user mapping for authentication plugins that request it. With
check_proxy_usersenabled, it may also be necessary to enable plugin-specific system variables to take advantage of server proxy user mapping support:For the
mysql_native_passwordplugin, enablemysql_native_password_proxy_users.For the
sha256_passwordplugin, enablesha256_password_proxy_users.
For information about user proxying, see Section 7.3.9, “Proxy Users”.
This variable was added in MySQL 5.7.7. Before 5.7.7, proxy user mapping is available only for plugins that implement it for themselves.
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System Variable Name collation_connectionVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringThe collation of the connection character set.
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System Variable Name collation_databaseVariable Scope Global, Session Dynamic Variable Yes Footnote This option is dynamic, but only the server should set this information. You should not set the value of this variable manually. Permitted Values Type stringThe collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as
collation_server.The global
character_set_databaseandcollation_databasesystem variables are deprecated as of MySQL 5.7.6 and will be removed in a future version of MySQL.Assigning a value to the session
character_set_databaseandcollation_databasesystem variables is deprecated as of MySQL 5.7.6 and assignments produce a warning. The session variables will become read only in a future version of MySQL and assignments will produce an error. It will remain possible to access the session variables to determine the database character set and collation for the default database. -
Command-Line Format --collation-serverSystem Variable Name collation_serverVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringDefault latin1_swedish_ciThe server's default collation.
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Command-Line Format --completion_type=#System Variable Name completion_typeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type enumerationDefault NO_CHAINValid Values NO_CHAINCHAINRELEASE012The transaction completion type. This variable can take the values shown in the following table. The variable can be assigned using either the name values or corresponding integer values.
Value Description NO_CHAIN(or 0)COMMITandROLLBACKare unaffected. This is the default value.CHAIN(or 1)COMMITandROLLBACKare equivalent toCOMMIT AND CHAINandROLLBACK AND CHAIN, respectively. (A new transaction starts immediately with the same isolation level as the just-terminated transaction.)RELEASE(or 2)COMMITandROLLBACKare equivalent toCOMMIT RELEASEandROLLBACK RELEASE, respectively. (The server disconnects after terminating the transaction.)completion_typeaffects transactions that begin withSTART TRANSACTIONorBEGINand end withCOMMITorROLLBACK. It does not apply to implicit commits resulting from execution of the statements listed in Section 14.3.3, “Statements That Cause an Implicit Commit”. It also does not apply forXA COMMIT,XA ROLLBACK, or whenautocommit=1. -
Command-Line Format --concurrent_insert[=#]System Variable Name concurrent_insertVariable Scope Global Dynamic Variable Yes Permitted Values Type enumerationDefault AUTOValid Values NEVERAUTOALWAYS012If
AUTO(the default), MySQL permitsINSERTandSELECTstatements to run concurrently forMyISAMtables that have no free blocks in the middle of the data file. If you start mysqld with--skip-new, this variable is set toNEVER.This variable can take the values shown in the following table. The variable can be assigned using either the name values or corresponding integer values.
Value Description NEVER(or 0)Disables concurrent inserts AUTO(or 1)(Default) Enables concurrent insert for MyISAMtables that do not have holesALWAYS(or 2)Enables concurrent inserts for all MyISAMtables, even those that have holes. For a table with a hole, new rows are inserted at the end of the table if it is in use by another thread. Otherwise, MySQL acquires a normal write lock and inserts the row into the hole.See also Section 9.11.3, “Concurrent Inserts”.
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Command-Line Format --connect_timeout=#System Variable Name connect_timeoutVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 10Min Value 2Max Value 31536000The number of seconds that the mysqld server waits for a connect packet before responding with
Bad handshake. The default value is 10 seconds.Increasing the
connect_timeoutvalue might help if clients frequently encounter errors of the formLost connection to MySQL server at '.XXX', system error:errno -
System Variable Name core_fileVariable Scope Global Dynamic Variable No Permitted Values Type booleanDefault OFFWhether to write a core file if the server crashes. This variable is set by the
--core-fileoption. -
Command-Line Format --datadir=dir_nameSystem Variable Name datadirVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe MySQL data directory. This variable can be set with the
--datadiroption. This variable is unused. It is deprecated and will be removed in a future MySQL release.
This variable is unused. It is deprecated and will be removed in a future MySQL release.
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Command-Line Format --debug[=debug_options]System Variable Name debugVariable Scope Global, Session Dynamic Variable Yes Permitted Values (Unix) Type stringDefault d:t:i:o,/tmp/mysqld.tracePermitted Values (Windows) Type stringDefault d:t:i:O,\mysqld.traceThis variable indicates the current debugging settings. It is available only for servers built with debugging support. The initial value comes from the value of instances of the
--debugoption given at server startup. The global and session values may be set at runtime; theSUPERprivilege is required, even for the session value.Assigning a value that begins with
+or-cause the value to added to or subtracted from the current value:mysql>
SET debug = 'T';mysql>SELECT @@debug;+---------+ | @@debug | +---------+ | T | +---------+ mysql>SET debug = '+P';mysql>SELECT @@debug;+---------+ | @@debug | +---------+ | P:T | +---------+ mysql>SET debug = '-P';mysql>SELECT @@debug;+---------+ | @@debug | +---------+ | T | +---------+For more information, see Section 26.5.3, “The DBUG Package”.
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System Variable Name debug_syncVariable Scope Session Dynamic Variable Yes Permitted Values Type stringThis variable is the user interface to the Debug Sync facility. Use of Debug Sync requires that MySQL be configured with the
-DENABLE_DEBUG_SYNC=1CMake option (see Section 2.9.4, “MySQL Source-Configuration Options”). If Debug Sync is not compiled in, this system variable is not available.The global variable value is read only and indicates whether the facility is enabled. By default, Debug Sync is disabled and the value of
debug_syncisOFF. If the server is started with--debug-sync-timeout=, whereNNis a timeout value greater than 0, Debug Sync is enabled and the value ofdebug_syncisON - current signalfollowed by the signal name. Also,Nbecomes the default timeout for individual synchronization points.The session value can be read by any user and will have the same value as the global variable. The session value can be set by users that have the
SUPERprivilege to control synchronization points.For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.
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Introduced 5.7.2 Command-Line Format --default-authentication-plugin=plugin_nameSystem Variable Name default_authentication_pluginVariable Scope Global Dynamic Variable No Permitted Values Type enumerationDefault mysql_native_passwordValid Values mysql_native_passwordsha256_passwordThe default authentication plugin. Permitted values are
mysql_native_password(use MySQL native passwords; this is the default) andsha256_password(use SHA-256 passwords). For more information about these plugins, see Section 7.5.1.1, “The Native Authentication Plugin”, and Section 7.5.1.4, “The SHA-256 Authentication Plugin”.NoteIf you use this variable to change the default authentication plugin to a value other than
mysql_native_password, clients older than MySQL 5.5.6 will no longer be able to connect because they will not understand the resulting change to the authentication protocol.The value of
default_authentication_pluginaffects these aspects of server operation:It determines which authentication plugin the server assigns to new accounts created by
CREATE USERandGRANTstatements that do not name a plugin explicitly with anIDENTIFIED WITHclause.It sets the
old_passwordssystem variable at startup to the value that is consistent with the password hashing method required by the default plugin. Theold_passwordsvalue affects hashing of passwords specified in theIDENTIFIED BYclause ofCREATE USERandGRANT, and passwords specified as the argument to thePASSWORD()function.For an account created with either of the following statements, the server associates the account with the default authentication plugin and assigns the account the given password, hashed according to the value of
old_passwords.CREATE USER ... IDENTIFIED BY '
cleartext password'; GRANT ... IDENTIFIED BY 'cleartext password';For an account created with either of the following statements, the statement fails if the password hash is not encrypted using the hash format required by the default authentication plugin. Otherwise, the server associates the account with the default authentication plugin and assigns the account the given password hash.
CREATE USER ... IDENTIFIED BY PASSWORD '
encrypted password'; GRANT ... IDENTIFIED BY PASSWORD 'encrypted password';
This variable was added in MySQL 5.7.2. Earlier in MySQL 5.7, use the
--default-authentication-plugincommand-line option instead, which is used the same way at server startup, but cannot be accessed at runtime. -
Introduced 5.7.4 Command-Line Format --default_password_lifetime=#System Variable Name default_password_lifetimeVariable Scope Global Dynamic Variable Yes Permitted Values (<= 5.7.10) Type integerDefault 360Min Value 0Max Value 65535Permitted Values (>= 5.7.11) Type integerDefault 0Min Value 0Max Value 65535This variable defines the global automatic password expiration policy. It applies to accounts that use MySQL built-in authentication methods (accounts that use an authentication plugin of
mysql_native_password,mysql_old_password, orsha256_password).The default
default_password_lifetimevalue is 0, which disables automatic password expiration. If the value ofdefault_password_lifetimeis a positive integerN, it indicates the permitted password lifetime; passwords must be changed everyNdays.The global password expiration policy can be overridden as desired for individual accounts using the
ALTER USERstatement. See Section 7.3.6, “Password Expiration Policy”.NoteFrom MySQL 5.7.4 to 5.7.10, the default
default_password_lifetimevalue is 360 (passwords must be changed approximately once per year). For those versions, be aware that, if you make no changes to thedefault_password_lifetimevariable or to individual user accounts, all user passwords will expire after 360 days, and all user accounts will start running in restricted mode when this happens. Clients (which are effectively users) connecting to the server will then get an error indicating that the password must be changed:ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.However, this is easy to miss for clients that automatically connect to the server, such as connections made from scripts. To avoid having such clients suddenly stop working due to a password expiring, make sure to change the password expiration settings for those clients, like this:
ALTER USER 'script'@'localhost' PASSWORD EXPIRE NEVER
Alternatively, set the
default_password_lifetimevariable to0, thus disabling automatic password expiration for all users. -
Command-Line Format --default-storage-engine=nameSystem Variable Name default_storage_engineVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type enumerationDefault InnoDBThe default storage engine. This variable sets the storage engine for permanent tables only. To set the storage engine for
TEMPORARYtables, set thedefault_tmp_storage_enginesystem variable.To see which storage engines are available and enabled, use the
SHOW ENGINESstatement or query theINFORMATION_SCHEMAENGINEStable.default_storage_engineshould be used in preference tostorage_engine, which is deprecated and was removed in MySQL 5.7.5.If you disable the default storage engine at server startup, you must set the default engine for both permanent and
TEMPORARYtables to a different engine or the server will not start. -
Command-Line Format --default_tmp_storage_engine=nameSystem Variable Name default_tmp_storage_engineVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type enumerationDefault InnoDBThe default storage engine for
TEMPORARYtables (created withCREATE TEMPORARY TABLE). To set the storage engine for permanent tables, set thedefault_storage_enginesystem variable. Also see the discussion of that variable regarding possible values.If you disable the default storage engine at server startup, you must set the default engine for both permanent and
TEMPORARYtables to a different engine or the server will not start. -
Command-Line Format --default_week_format=#System Variable Name default_week_formatVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 0Min Value 0Max Value 7The default mode value to use for the
WEEK()function. See Section 13.7, “Date and Time Functions”. -
Command-Line Format --delay-key-write[=name]System Variable Name delay_key_writeVariable Scope Global Dynamic Variable Yes Permitted Values Type enumerationDefault ONValid Values ONOFFALLThis option applies only to
MyISAMtables. It can have one of the following values to affect handling of theDELAY_KEY_WRITEtable option that can be used inCREATE TABLEstatements.Option Description OFFDELAY_KEY_WRITEis ignored.ONMySQL honors any DELAY_KEY_WRITEoption specified inCREATE TABLEstatements. This is the default value.ALLAll new opened tables are treated as if they were created with the DELAY_KEY_WRITEoption enabled.If
DELAY_KEY_WRITEis enabled for a table, the key buffer is not flushed for the table on every index update, but only when the table is closed. This speeds up writes on keys a lot, but if you use this feature, you should add automatic checking of allMyISAMtables by starting the server with the--myisam-recover-optionsoption (for example,--myisam-recover-options=BACKUP,FORCE). See Section 6.1.3, “Server Command Options”, and Section 16.2.1, “MyISAM Startup Options”.WarningIf you enable external locking with
--external-locking, there is no protection against index corruption for tables that use delayed key writes. -
Deprecated 5.6.7 Command-Line Format --delayed_insert_limit=#System Variable Name delayed_insert_limitVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 100Min Value 1Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 100Min Value 1Max Value 18446744073709551615This system variable is deprecated (because
DELAYEDinserts are not supported), and will be removed in a future release. -
Deprecated 5.6.7 Command-Line Format --delayed_insert_timeout=#System Variable Name delayed_insert_timeoutVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 300This system variable is deprecated (because
DELAYEDinserts are not supported), and will be removed in a future release. -
Deprecated 5.6.7 Command-Line Format --delayed_queue_size=#System Variable Name delayed_queue_sizeVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 1000Min Value 1Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 1000Min Value 1Max Value 18446744073709551615This system variable is deprecated (because
DELAYEDinserts are not supported), and will be removed in a future release. -
Introduced 5.7.8 Command-Line Format --disabled_storage_engines=engine[,engine]...System Variable Name disabled_storage_enginesVariable Scope Global Dynamic Variable No Permitted Values Type stringDefault empty stringThis variable indicates which storage engines cannot be used to create tables or tablespaces. For example, to prevent new
MyISAMorFEDERATEDtables from being created, start the server with these lines in the server option file:[mysqld] disabled_storage_engines="MyISAM,FEDERATED"
By default,
disabled_storage_enginesis empty (no engines disabled), but it can be set to a comma-separated list of one or more engines (not case sensitive). Any engine named in the value cannot be used to create tables or tablespaces withCREATE TABLEorCREATE TABLESPACE, and cannot be used withALTER TABLE ... ENGINEorALTER TABLESPACE ... ENGINEto change the storage engine of existing tables or tablespaces. Attempts to do so result in anER_DISABLED_STORAGE_ENGINEerror.disabled_storage_enginesdoes not restrict other DDL statements for existing tables, such asCREATE INDEX,TRUNCATE TABLE,ANALYZE TABLE,DROP TABLE, orDROP TABLESPACE. This permits a smooth transition so that existing tables or tablespaces that use a disabled engine can be migrated to a permitted engine by means such asALTER TABLE ... ENGINE.permitted_engineIt is permitted to set the
default_storage_engineordefault_tmp_storage_enginesystem variable to a storage engine that is disabled. This could cause applications to behave erratically or fail, although that might be a useful technique in a development environment for identifying applications that use disabled engines, so that they can be modified.disabled_storage_enginesis disabled and has no effect if the server is started with any of these options:--bootstrap,--initialize,--initialize-insecure,--skip-grant-tables. disconnect_on_expired_passwordIntroduced 5.7.1 Command-Line Format --disconnect_on_expired_password[=#]System Variable Name disconnect_on_expired_passwordVariable Scope Session Dynamic Variable No Permitted Values Type booleanDefault ONThis variable controls how the server handles clients with expired passwords:
If the client indicates that it can handle expires passwords, the value of
disconnect_on_expired_passwordis irrelevant. The server permits the client to connect but puts it in sandbox mode.If the client does not indicate that it can handle expires passwords, the server handles the client according to the value of
disconnect_on_expired_password:If
disconnect_on_expired_password: is enabled, the server disconnects the client.If
disconnect_on_expired_password: is disabled, the server permits the client to connect but puts it in sandbox mode.
For more information about the interaction of client and server settings relating to expired-password handling, see Section 7.3.7, “Password Expiration and Sandbox Mode”.
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Command-Line Format --div_precision_increment=#System Variable Name div_precision_incrementVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 4Min Value 0Max Value 30This variable indicates the number of digits by which to increase the scale of the result of division operations performed with the
/operator. The default value is 4. The minimum and maximum values are 0 and 30, respectively. The following example illustrates the effect of increasing the default value.mysql>
SELECT 1/7;+--------+ | 1/7 | +--------+ | 0.1429 | +--------+ mysql>SET div_precision_increment = 12;mysql>SELECT 1/7;+----------------+ | 1/7 | +----------------+ | 0.142857142857 | +----------------+ -
System Variable Name end_markers_in_jsonVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault OFFWhether optimizer JSON output should add end markers.
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System Variable Name eq_range_index_dive_limitVariable Scope Global, Session Dynamic Variable Yes Permitted Values (<= 5.7.3) Type integerDefault 10Min Value 0Max Value 4294967295Permitted Values (>= 5.7.4) Type integerDefault 200Min Value 0Max Value 4294967295This variable indicates the number of equality ranges in an equality comparison condition when the optimizer should switch from using index dives to index statistics in estimating the number of qualifying rows. It applies to evaluation of expressions that have either of these equivalent forms, where the optimizer uses a nonunique index to look up
col_namevalues:col_nameIN(val1, ...,valN)col_name=val1OR ... ORcol_name=valNIn both cases, the expression contains
Nequality ranges. The optimizer can make row estimates using index dives or index statistics. Ifeq_range_index_dive_limitis greater than 0, the optimizer uses existing index statistics instead of index dives if there areeq_range_index_dive_limitor more equality ranges. Thus, to permit use of index dives for up toNequality ranges, seteq_range_index_dive_limittoN+ 1. To disable use of index statistics and always use index dives regardless ofN, seteq_range_index_dive_limitto 0.For more information, see Section 9.2.1.3.3, “Equality Range Optimization of Many-Valued Comparisons”.
To update table index statistics for best estimates, use
ANALYZE TABLE. The number of errors that resulted from the last statement that generated messages. This variable is read only. See Section 14.7.5.17, “SHOW ERRORS Syntax”.
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Command-Line Format --event-scheduler[=value]System Variable Name event_schedulerVariable Scope Global Dynamic Variable Yes Permitted Values Type enumerationDefault OFFValid Values ONOFFDISABLEDThis variable indicates the status of the Event Scheduler; possible values are
ON,OFF, andDISABLED, with the default beingOFF. This variable and its effects on the Event Scheduler's operation are discussed in greater detail in the Overview section of the Events chapter. -
Command-Line Format --expire_logs_days=#System Variable Name expire_logs_daysVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 0Min Value 0Max Value 99The number of days for automatic binary log file removal. The default is 0, which means “no automatic removal.” Possible removals happen at startup and when the binary log is flushed. Log flushing occurs as indicated in Section 6.4, “MySQL Server Logs”.
To remove binary log files manually, use the
PURGE BINARY LOGSstatement. See Section 14.4.1.1, “PURGE BINARY LOGS Syntax”. explicit_defaults_for_timestampDeprecated 5.6.6 Command-Line Format --explicit_defaults_for_timestamp=#System Variable Name explicit_defaults_for_timestampVariable Scope Global, Session Dynamic Variable No Permitted Values Type booleanDefault FALSEIn MySQL, the
TIMESTAMPdata type differs in nonstandard ways from other data types:TIMESTAMPcolumns not explicitly declared with theNULLattribute are assigned theNOT NULLattribute. (Columns of other data types, if not explicitly declared asNOT NULL, permitNULLvalues.) Setting such a column toNULLsets it to the current timestamp.The first
TIMESTAMPcolumn in a table, if not declared with theNULLattribute or an explicitDEFAULTorON UPDATEclause, is automatically assigned theDEFAULT CURRENT_TIMESTAMPandON UPDATE CURRENT_TIMESTAMPattributes.TIMESTAMPcolumns following the first one, if not declared with theNULLattribute or an explicitDEFAULTclause, are automatically assignedDEFAULT '0000-00-00 00:00:00'(the “zero” timestamp). For inserted rows that specify no explicit value for such a column, the column is assigned'0000-00-00 00:00:00'and no warning occurs.
Those nonstandard behaviors remain the default for
TIMESTAMPbut as of MySQL 5.6.6 are deprecated and this warning appears at startup:[Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
As indicated by the warning, to turn off the nonstandard behaviors, enable the
explicit_defaults_for_timestampsystem variable at server startup. With this variable enabled, the server handlesTIMESTAMPas follows instead:TIMESTAMPcolumns not explicitly declared asNOT NULLpermitNULLvalues. Setting such a column toNULLsets it toNULL, not the current timestamp.No
TIMESTAMPcolumn is assigned theDEFAULT CURRENT_TIMESTAMPorON UPDATE CURRENT_TIMESTAMPattributes automatically. Those attributes must be explicitly specified.TIMESTAMPcolumns declared asNOT NULLand without an explicitDEFAULTclause are treated as having no default value. For inserted rows that specify no explicit value for such a column, the result depends on the SQL mode. If strict SQL mode is enabled, an error occurs. If strict SQL mode is not enabled, the column is assigned the implicit default of'0000-00-00 00:00:00'and a warning occurs. This is similar to how MySQL treats other temporal types such asDATETIME.
Noteexplicit_defaults_for_timestampis itself deprecated because its only purpose is to permit control over now-deprecatedTIMESTAMPbehaviors that will be removed in a future MySQL release. When that removal occurs,explicit_defaults_for_timestampwill have no purpose and will be removed as well.-
System Variable Name external_userVariable Scope Session Dynamic Variable No Permitted Values Type stringThe external user name used during the authentication process, as set by the plugin used to authenticate the client. With native (built-in) MySQL authentication, or if the plugin does not set the value, this variable is
NULL. See Section 7.3.9, “Proxy Users”. -
Command-Line Format --flushSystem Variable Name flushVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFIf
ON, the server flushes (synchronizes) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.5.3.3, “What to Do If MySQL Keeps Crashing”. This variable is set toONif you start mysqld with the--flushoption. -
Command-Line Format --flush_time=#System Variable Name flush_timeVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 0Min Value 0Permitted Values (Windows) Type integerDefault 0Min Value 0If this is set to a nonzero value, all tables are closed every
flush_timeseconds to free up resources and synchronize unflushed data to disk. This option is best used only on systems with minimal resources. If set to 1 (the default), foreign key constraints for
InnoDBtables are checked. If set to 0, foreign key constraints are ignored, with a couple of exceptions. When re-creating a table that was dropped, an error is returned if the table definition does not conform to the foreign key constraints referencing the table. Likewise, anALTER TABLEoperation returns an error if a foreign key definition is incorrectly formed. For more information, see Section 14.1.18.3, “Using FOREIGN KEY Constraints”.Setting this variable has the same effect on
NDBtables as it does forInnoDBtables. Typically you leave this setting enabled during normal operation, to enforce referential integrity. Disabling foreign key checking can be useful for reloadingInnoDBtables in an order different from that required by their parent/child relationships. See Section 15.8.7, “InnoDB and FOREIGN KEY Constraints”.Setting
foreign_key_checksto 0 also affects data definition statements:DROP SCHEMAdrops a schema even if it contains tables that have foreign keys that are referred to by tables outside the schema, andDROP TABLEdrops tables that have foreign keys that are referred to by other tables.NoteSetting
foreign_key_checksto 1 does not trigger a scan of the existing table data. Therefore, rows added to the table whileforeign_key_checks=0will not be verified for consistency.As of MySQL 5.7.5, dropping an index required by a foreign key constraint is not permitted, even with
foreign_key_checks=0. The foreign key constraint must be removed before dropping the index (Bug #70260).-
Command-Line Format --ft_boolean_syntax=nameSystem Variable Name ft_boolean_syntaxVariable Scope Global Dynamic Variable Yes Permitted Values Type stringDefault + -><()~*:""&|The list of operators supported by boolean full-text searches performed using
IN BOOLEAN MODE. See Section 13.9.2, “Boolean Full-Text Searches”.The default variable value is
'+ -><()~*:""&|'. The rules for changing the value are as follows:Operator function is determined by position within the string.
The replacement value must be 14 characters.
Each character must be an ASCII nonalphanumeric character.
Either the first or second character must be a space.
No duplicates are permitted except the phrase quoting operators in positions 11 and 12. These two characters are not required to be the same, but they are the only two that may be.
Positions 10, 13, and 14 (which by default are set to “
:”, “&”, and “|”) are reserved for future extensions.
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Command-Line Format --ft_max_word_len=#System Variable Name ft_max_word_lenVariable Scope Global Dynamic Variable No Permitted Values Type integerMin Value 10The maximum length of the word to be included in a
MyISAMFULLTEXTindex.NoteFULLTEXTindexes onMyISAMtables must be rebuilt after changing this variable. UseREPAIR TABLE.tbl_nameQUICK -
Command-Line Format --ft_min_word_len=#System Variable Name ft_min_word_lenVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 4Min Value 1The minimum length of the word to be included in a
MyISAMFULLTEXTindex.NoteFULLTEXTindexes onMyISAMtables must be rebuilt after changing this variable. UseREPAIR TABLE.tbl_nameQUICK -
Command-Line Format --ft_query_expansion_limit=#System Variable Name ft_query_expansion_limitVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 20Min Value 0Max Value 1000The number of top matches to use for full-text searches performed using
WITH QUERY EXPANSION. -
Command-Line Format --ft_stopword_file=file_nameSystem Variable Name ft_stopword_fileVariable Scope Global Dynamic Variable No Permitted Values Type file nameThe file from which to read the list of stopwords for full-text searches on
MyISAMtables. The server looks for the file in the data directory unless an absolute path name is given to specify a different directory. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in thestorage/myisam/ft_static.cfile). Setting this variable to the empty string ('') disables stopword filtering. See also Section 13.9.4, “Full-Text Stopwords”.NoteFULLTEXTindexes onMyISAMtables must be rebuilt after changing this variable or the contents of the stopword file. UseREPAIR TABLE.tbl_nameQUICK -
Command-Line Format --general-logSystem Variable Name general_logVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFWhether the general query log is enabled. The value can be 0 (or
OFF) to disable the log or 1 (orON) to enable the log. The default value depends on whether the--general_logoption is given. The destination for log output is controlled by thelog_outputsystem variable; if that value isNONE, no log entries are written even if the log is enabled. -
Command-Line Format --general-log-file=file_nameSystem Variable Name general_log_fileVariable Scope Global Dynamic Variable Yes Permitted Values Type file nameDefault host_name.logThe name of the general query log file. The default value is
host_name.log--general_log_fileoption. -
Command-Line Format --group_concat_max_len=#System Variable Name group_concat_max_lenVariable Scope Global, Session Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 1024Min Value 4Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 1024Min Value 4Max Value 18446744073709551615The maximum permitted result length in bytes for the
GROUP_CONCAT()function. The default is 1024. YESif thezlibcompression library is available to the server,NOif not. If not, theCOMPRESS()andUNCOMPRESS()functions cannot be used.YESif thecrypt()system call is available to the server,NOif not. If not, theENCRYPT()function cannot be used.YESif mysqld supports dynamic loading of plugins,NOif not. If the value isNO, you cannot use options such as--plugin-loadto load plugins at server startup, or theINSTALL PLUGINstatement to load plugins at runtime.YESif the server supports spatial data types,NOif not.This variable is an alias for
have_ssl.YESif statement profiling capability is present,NOif not. If present, theprofilingsystem variable controls whether this capability is enabled or disabled. See Section 14.7.5.31, “SHOW PROFILES Syntax”.This variable is deprecated and will be removed in a future MySQL release.
YESif mysqld supports the query cache,NOif not.YESifRTREEindexes are available,NOif not. (These are used for spatial indexes inMyISAMtables.)YESif mysqld supports SSL connections,NOif not.DISABLEDindicates that the server was compiled with SSL support, but was not started with the appropriate--ssl-options. For more information, see Section 7.4.2, “Building MySQL with Support for Secure Connections”.xxx-
Introduced 5.7.4 System Variable Name have_statement_timeoutVariable Scope Global Dynamic Variable No Permitted Values Type booleanWhether the statement execution timeout feature is available (see Statement Execution Time Optimizer Hints). The value can be
NOif the background thread used by this feature could not be initialized. YESif symbolic link support is enabled,NOif not. This is required on Unix for support of theDATA DIRECTORYandINDEX DIRECTORYtable options. If the server is started with the--skip-symbolic-linksoption, the value isDISABLED.This variable has no meaning on Windows.
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System Variable Name host_cache_sizeVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault -1 (autosized)Min Value 0Max Value 65536The size of the internal host cache (see Section 9.12.6.2, “DNS Lookup Optimization and the Host Cache”). Setting the size to 0 disables the host cache. Changing the cache size at runtime implicitly causes a
FLUSH HOSTSoperation to clear the host cache and truncate thehost_cachetable.The default value is 128, plus 1 for a value of
max_connectionsup to 500, plus 1 for every increment of 20 over 500 in themax_connectionsvalue, capped to a limit of 2000.Use of
--skip-host-cacheis similar to setting thehost_cache_sizesystem variable to 0, buthost_cache_sizeis more flexible because it can also be used to resize, enable, or disable the host cache at runtime, not just at server startup.If you start the server with
--skip-host-cache, that does not prevent changes to the value ofhost_cache_size, but such changes have no effect and the cache is not re-enabled even ifhost_cache_sizeis set larger than 0. -
System Variable Name hostnameVariable Scope Global Dynamic Variable No Permitted Values Type stringThe server sets this variable to the server host name at startup.
This variable is a synonym for the
last_insert_idvariable. It exists for compatibility with other database systems. You can read its value withSELECT @@identity, and set it usingSET identity.-
System Variable Name ignore_db_dirsVariable Scope Global Dynamic Variable No Permitted Values Type stringA comma-separated list of names that are not considered as database directories in the data directory. The value is set from any instances of
--ignore-db-dirgiven at server startup.As of MySQL 5.7.11,
--ignore-db-dircan be used at data directory initialization time with mysqld --initialize to specify directories that the server should ignore for purposes of assessing whether an existing data directory is considered empty. See Section 2.10.1.1, “Initializing the Data Directory Manually Using mysqld”. -
Command-Line Format --init-connect=nameSystem Variable Name init_connectVariable Scope Global Dynamic Variable Yes Permitted Values Type stringA string to be executed by the server for each client that connects. The string consists of one or more SQL statements, separated by semicolon characters. For example, each client session begins by default with autocommit mode enabled. For older servers (before MySQL 5.5.8), there is no global
autocommitsystem variable to specify that autocommit should be disabled by default, but as a workaroundinit_connectcan be used to achieve the same effect:SET GLOBAL init_connect='SET autocommit=0';
The
init_connectvariable can also be set on the command line or in an option file. To set the variable as just shown using an option file, include these lines:[mysqld] init_connect='SET autocommit=0'
The content of
init_connectis not executed for users that have theSUPERprivilege. This is done so that an erroneous value forinit_connectdoes not prevent all clients from connecting. For example, the value might contain a statement that has a syntax error, thus causing client connections to fail. Not executinginit_connectfor users that have theSUPERprivilege enables them to open a connection and fix theinit_connectvalue.The server discards any result sets produced by statements in the value of of
init_connect. -
Command-Line Format --init-file=file_nameSystem Variable Name init_fileVariable Scope Global Dynamic Variable No Permitted Values Type file nameThe name of the file specified with the
--init-fileoption when you start the server. This should be a file containing SQL statements that you want the server to execute when it starts. Each statement must be on a single line and should not include comments. For more information, see the description of--init-file. innodb_xxxInnoDBsystem variables are listed in Section 15.14, “InnoDB Startup Options and System Variables”. These variables control many aspects of storage, memory use, and I/O patterns forInnoDBtables, and are especially important now thatInnoDBis the default storage engine.The value to be used by the following
INSERTorALTER TABLEstatement when inserting anAUTO_INCREMENTvalue. This is mainly used with the binary log.-
Command-Line Format --interactive_timeout=#System Variable Name interactive_timeoutVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 28800Min Value 1The number of seconds the server waits for activity on an interactive connection before closing it. An interactive client is defined as a client that uses the
CLIENT_INTERACTIVEoption tomysql_real_connect(). See alsowait_timeout. internal_tmp_disk_storage_engineIntroduced 5.7.5 Command-Line Format --internal_tmp_disk_storage_engine=#System Variable Name internal_tmp_disk_storage_engineVariable Scope Global Dynamic Variable Yes Permitted Values (5.7.5) Type enumerationDefault MYISAMValid Values MYISAMINNODBPermitted Values (>= 5.7.6) Type enumerationDefault INNODBValid Values MYISAMINNODBThe storage engine for on-disk internal temporary tables (see Section 9.4.4, “Internal Temporary Table Use in MySQL”). Permitted values are
MYISAMandINNODB.This variable was added in MySQL 5.7.5 with a default of
MYISAM. In MySQL 5.7.6, the default value was changed toINNODB. With this change, the optimizer uses theInnoDBstorage engine by default for on-disk internal temporary tables.Under
internal_tmp_disk_storage_engine=INNODB, queries that generate temporary tables that exceedInnoDBrow or column limits will return Row size too large or Too many columns errors. The workaround is to setinternal_tmp_disk_storage_enginetoMYISAM.-
Command-Line Format --join_buffer_size=#System Variable Name join_buffer_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (Windows) Type integerDefault 262144Min Value 128Max Value 4294967295Permitted Values (Other, 32-bit platforms) Type integerDefault 262144Min Value 128Max Value 4294967295Permitted Values (Other, 64-bit platforms) Type integerDefault 262144Min Value 128Max Value 18446744073709547520The minimum size of the buffer that is used for plain index scans, range index scans, and joins that do not use indexes and thus perform full table scans. Normally, the best way to get fast joins is to add indexes. Increase the value of
join_buffer_sizeto get a faster full join when adding indexes is not possible. One join buffer is allocated for each full join between two tables. For a complex join between several tables for which indexes are not used, multiple join buffers might be necessary.Unless Batched Key Access (BKA) is used, there is no gain from setting the buffer larger than required to hold each matching row, and all joins allocate at least the minimum size, so use caution in setting this variable to a large value globally. It is better to keep the global setting small and change to a larger setting only in sessions that are doing large joins. Memory allocation time can cause substantial performance drops if the global size is larger than needed by most queries that use it.
When BKA is used, the value of
join_buffer_sizedefines how large the batch of keys is in each request to the storage engine. The larger the buffer, the more sequential access will be to the right hand table of a join operation, which can significantly improve performance.The default is 256KB. The maximum permissible setting for
join_buffer_sizeis 4GB−1. Larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB−1 with a warning).For additional information about join buffering, see Section 9.2.1.10, “Nested-Loop Join Algorithms”. For information about Batched Key Access, see Section 9.2.1.14, “Block Nested-Loop and Batched Key Access Joins”.
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Command-Line Format --keep_files_on_create=#System Variable Name keep_files_on_createVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault OFFIf a
MyISAMtable is created with noDATA DIRECTORYoption, the.MYDfile is created in the database directory. By default, ifMyISAMfinds an existing.MYDfile in this case, it overwrites it. The same applies to.MYIfiles for tables created with noINDEX DIRECTORYoption. To suppress this behavior, set thekeep_files_on_createvariable toON(1), in which caseMyISAMwill not overwrite existing files and returns an error instead. The default value isOFF(0).If a
MyISAMtable is created with aDATA DIRECTORYorINDEX DIRECTORYoption and an existing.MYDor.MYIfile is found, MyISAM always returns an error. It will not overwrite a file in the specified directory. -
Command-Line Format --key_buffer_size=#System Variable Name key_buffer_sizeVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 8388608Min Value 8Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 8388608Min Value 8Max Value OS_PER_PROCESS_LIMITIndex blocks for
MyISAMtables are buffered and are shared by all threads.key_buffer_sizeis the size of the buffer used for index blocks. The key buffer is also known as the key cache.The maximum permissible setting for
key_buffer_sizeis 4GB−1 on 32-bit platforms. Larger values are permitted for 64-bit platforms. The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform. The value of this variable indicates the amount of memory requested. Internally, the server allocates as much memory as possible up to this amount, but the actual allocation might be less.You can increase the value to get better index handling for all reads and multiple writes; on a system whose primary function is to run MySQL using the
MyISAMstorage engine, 25% of the machine's total memory is an acceptable value for this variable. However, you should be aware that, if you make the value too large (for example, more than 50% of the machine's total memory), your system might start to page and become extremely slow. This is because MySQL relies on the operating system to perform file system caching for data reads, so you must leave some room for the file system cache. You should also consider the memory requirements of any other storage engines that you may be using in addition toMyISAM.For even more speed when writing many rows at the same time, use
LOCK TABLES. See Section 9.2.2.1, “Speed of INSERT Statements”.You can check the performance of the key buffer by issuing a
SHOW STATUSstatement and examining theKey_read_requests,Key_reads,Key_write_requests, andKey_writesstatus variables. (See Section 14.7.5, “SHOW Syntax”.) TheKey_reads/Key_read_requestsratio should normally be less than 0.01. TheKey_writes/Key_write_requestsratio is usually near 1 if you are using mostly updates and deletes, but might be much smaller if you tend to do updates that affect many rows at the same time or if you are using theDELAY_KEY_WRITEtable option.The fraction of the key buffer in use can be determined using
key_buffer_sizein conjunction with theKey_blocks_unusedstatus variable and the buffer block size, which is available from thekey_cache_block_sizesystem variable:1 - ((Key_blocks_unused * key_cache_block_size) / key_buffer_size)
This value is an approximation because some space in the key buffer is allocated internally for administrative structures. Factors that influence the amount of overhead for these structures include block size and pointer size. As block size increases, the percentage of the key buffer lost to overhead tends to decrease. Larger blocks results in a smaller number of read operations (because more keys are obtained per read), but conversely an increase in reads of keys that are not examined (if not all keys in a block are relevant to a query).
It is possible to create multiple
MyISAMkey caches. The size limit of 4GB applies to each cache individually, not as a group. See Section 9.10.2, “The MyISAM Key Cache”. -
Command-Line Format --key_cache_age_threshold=#System Variable Name key_cache_age_thresholdVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 300Min Value 100Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 300Min Value 100Max Value 18446744073709551615This value controls the demotion of buffers from the hot sublist of a key cache to the warm sublist. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 9.10.2, “The MyISAM Key Cache”.
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Command-Line Format --key_cache_block_size=#System Variable Name key_cache_block_sizeVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 1024Min Value 512Max Value 16384The size in bytes of blocks in the key cache. The default value is 1024. See Section 9.10.2, “The MyISAM Key Cache”.
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Command-Line Format --key_cache_division_limit=#System Variable Name key_cache_division_limitVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 100Min Value 1Max Value 100The division point between the hot and warm sublists of the key cache buffer list. The value is the percentage of the buffer list to use for the warm sublist. Permissible values range from 1 to 100. The default value is 100. See Section 9.10.2, “The MyISAM Key Cache”.
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Introduced 5.7.11 Command-Line Format --keyring_file_data=file_nameSystem Variable Name keyring_file_dataVariable Scope Global Dynamic Variable Yes Permitted Values Type file nameDefault platform specificThe path name of the data file used for secure data storage by the
keyring_fileplugin (see Section 7.5.3.2, “Configuring the keyring_file File-Based Plugin”). The file location should be in a directory considered for use only by thekeyring_fileplugin. For example, do not locate the file under the data directory.Keyring operations are transactional: The
keyring_fileplugin uses a backup file during write operations to ensure that it can roll back to the original file if an operation fails. The backup file has the same name as the value of thekeyring_file_datasystem variable with an extension of.backup.Do not use the same
keyring_filedata file for multiple MySQL instances. Each instance should have its own unique data file.The default file name is
keyring, located in a directory that is platform specific and depends on the value of theINSTALL_LAYOUTCMake option, as shown in the following table. To specify the default directory for the file explicitly if you are building from source, use theINSTALL_MYSQLKEYRINGDIRCMake option.INSTALL_LAYOUTValueDefault keyring_file_dataValueDEB,RPM,SLES,SVR4/var/lib/mysql-keyring/keyringOtherwise keyring/keyringunder theCMAKE_INSTALL_PREFIXvalueIf the value assigned to
keyring_file_dataspecifies a file that does not exist, thekeyring_fileplugin attempts to create it during plugin initialization. If necessary, the plugin also creates the directory in which the file is located.If you create the directory manually, it should have a restrictive mode and be accessible only to the account used to run the server. For example, on Unix and Unix-like systems, to use
/usr/local/mysql/mysql-keyring/keyring, the following commands (executed asroot) create the directory and set its mode and ownership:shell>
cd /usr/local/mysqlshell>mkdir mysql-keyringshell>chmod 750 mysql-keyringshell>chown mysql mysql-keyringshell>chgrp mysql mysql-keyringIf the
keyring_fileplugin cannot create or access the file, it writes an error message to the error log. If an attempted runtime assignment tokeyring_file_dataresults in an error, the variable value remains unchanged.ImportantOnce the
keyring_fileplugin has created thekeyring_fileplugin data file and started to use it, it is important not to remove the file. For example,InnoDBuses the file to store the master key used to decrypt the data in tables that use tablespace encryption; see Section 15.7.10, “InnoDB Tablespace Encryption”. Loss of the file will cause data in such tables to become inaccessible. (It is permissible to rename or move the file, as long as you change the value ofkeyring_file_datato match.) It is recommended that you create a separate backup of thekeyringfile immediately after you create the first encrypted table and before and after master key rotation. -
Introduced 5.7.12 Command-Line Format --keyring_okv_conf_dir=dir_nameSystem Variable Name keyring_okv_conf_dirVariable Scope Global Dynamic Variable Yes Permitted Values Type directory nameDefault empty stringThe path name of the directory that stores configuration information used by the
keyring_okvplugin (see Section 7.5.3.3, “Configuring the keyring_okv Oracle Key Vault Plugin”). The location should be a directory considered for use only by thekeyring_okvplugin. For example, do not locate the directory under the data directory.The default
keyring_okv_conf_dirvalue is empty. For thekeyring_okvplugin to be able to access Oracle Key Vault, the value must be set to a directory that contains Oracle Key Vault configuration and SSL materials. For instructions on setting up this directory, see Section 7.5.3.3, “Configuring the keyring_okv Oracle Key Vault Plugin”.The directory should have a restrictive mode and be accessible only to the account used to run the server. For example, on Unix and Unix-like systems, to use
/usr/local/mysql/mysql-keyring-okv, the following commands (executed asroot) create the directory and set its mode and ownership:shell>
cd /usr/local/mysqlshell>mkdir mysql-keyring-okvshell>chmod 750 mysql-keyring-okvshell>chown mysql mysql-keyring-okvshell>chgrp mysql mysql-keyring-okvIf the value assigned to
keyring_okv_conf_dirspecifies a directory that does not exist, or that does not contain configuration information that enables a connection to Oracle Key Vault to be established,keyring_okvwrites an error message to the error log. If an attempted runtime assignment tokeyring_okv_conf_dirresults in an error, the variable value and keyring operation remain unchanged. -
System Variable Name large_files_supportVariable Scope Global Dynamic Variable No Whether mysqld was compiled with options for large file support.
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Command-Line Format --large-pagesSystem Variable Name large_pagesVariable Scope Global Dynamic Variable No Platform Specific Linux Permitted Values (Linux) Type booleanDefault FALSEWhether large page support is enabled (via the
--large-pagesoption). See Section 9.12.5.2, “Enabling Large Page Support”. -
System Variable Name large_page_sizeVariable Scope Global Dynamic Variable No Permitted Values (Linux) Type integerDefault 0If large page support is enabled, this shows the size of memory pages. Large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0. See Section 9.12.5.2, “Enabling Large Page Support”.
The value to be returned from
LAST_INSERT_ID(). This is stored in the binary log when you useLAST_INSERT_ID()in a statement that updates a table. Setting this variable does not update the value returned by themysql_insert_id()C API function.-
Command-Line Format --lc-messages=nameSystem Variable Name lc_messagesVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringDefault en_USThe locale to use for error messages. The default is
en_US. The server converts the argument to a language name and combines it with the value oflc_messages_dirto produce the location for the error message file. See Section 11.2, “Setting the Error Message Language”. -
Command-Line Format --lc-messages-dir=dir_nameSystem Variable Name lc_messages_dirVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe directory where error messages are located. The server uses the value together with the value of
lc_messagesto produce the location for the error message file. See Section 11.2, “Setting the Error Message Language”. -
System Variable Name lc_time_namesVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringThis variable specifies the locale that controls the language used to display day and month names and abbreviations. This variable affects the output from the
DATE_FORMAT(),DAYNAME()andMONTHNAME()functions. Locale names are POSIX-style values such as'ja_JP'or'pt_BR'. The default value is'en_US'regardless of your system's locale setting. For further information, see Section 11.7, “MySQL Server Locale Support”. -
System Variable Name licenseVariable Scope Global Dynamic Variable No Permitted Values Type stringDefault GPLThe type of license the server has.
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System Variable Name local_infileVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault trueWhether
LOCALis supported forLOAD DATA INFILEstatements. If this variable is disabled, clients cannot useLOCALinLOAD DATAstatements. While the default for this variable istrue, whetherLOAD DATA INFILE LOCALis actually permitted depends on how MySQL was compiled, as well as a number of settings on both the server and the client; see Section 7.1.6, “Security Issues with LOAD DATA LOCAL”, for details. -
Command-Line Format --lock_wait_timeout=#System Variable Name lock_wait_timeoutVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 31536000Min Value 1Max Value 31536000This variable specifies the timeout in seconds for attempts to acquire metadata locks. The permissible values range from 1 to 31536000 (1 year). The default is 31536000.
This timeout applies to all statements that use metadata locks. These include DML and DDL operations on tables, views, stored procedures, and stored functions, as well as
LOCK TABLES,FLUSH TABLES WITH READ LOCK, andHANDLERstatements.This timeout does not apply to implicit accesses to system tables in the
mysqldatabase, such as grant tables modified byGRANTorREVOKEstatements or table logging statements. The timeout does apply to system tables accessed directly, such as withSELECTorUPDATE.The timeout value applies separately for each metadata lock attempt. A given statement can require more than one lock, so it is possible for the statement to block for longer than the
lock_wait_timeoutvalue before reporting a timeout error. When lock timeout occurs,ER_LOCK_WAIT_TIMEOUTis reported.lock_wait_timeoutdoes not apply to delayed inserts, which always execute with a timeout of 1 year. This is done to avoid unnecessary timeouts because a session that issues a delayed insert receives no notification of delayed insert timeouts. -
System Variable Name locked_in_memoryVariable Scope Global Dynamic Variable No log_backward_compatible_user_definitionsIntroduced 5.7.6 Removed 5.7.9 Command-Line Format --log_backward_compatible_user_definitions[={OFF|ON}]System Variable Name log_backward_compatible_user_definitionsVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFWhether to log the
user_specificationpart ofCREATE USER,ALTER USER, andGRANTstatements in backward-compatible (pre-5.7.6) fashion:By default, this variable is disabled. The server writes user specifications as
userIDENTIFIED WITHauth_pluginAS 'hash_string'When enabled, the server writes user specifications as
userIDENTIFIED BY PASSWORD 'hash_string'
This variable was removed in MySQL 5.7.9 and replaced by
log_builtin_as_identified_by_password.log_bin_trust_function_creatorsCommand-Line Format --log-bin-trust-function-creatorsSystem Variable Name log_bin_trust_function_creatorsVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault FALSEThis variable applies when binary logging is enabled. It controls whether stored function creators can be trusted not to create stored functions that will cause unsafe events to be written to the binary log. If set to 0 (the default), users are not permitted to create or alter stored functions unless they have the
SUPERprivilege in addition to theCREATE ROUTINEorALTER ROUTINEprivilege. A setting of 0 also enforces the restriction that a function must be declared with theDETERMINISTICcharacteristic, or with theREADS SQL DATAorNO SQLcharacteristic. If the variable is set to 1, MySQL does not enforce these restrictions on stored function creation. This variable also applies to trigger creation. See Section 21.7, “Binary Logging of Stored Programs”.log_builtin_as_identified_by_passwordIntroduced 5.7.9 Command-Line Format --log_builtin_as_identified_by_password[={OFF|ON}]System Variable Name log_builtin_as_identified_by_passwordVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFThis variable affects binary logging of user-management statements. If enabled, binary logging for
CREATE USERstatements involving built-in authentication plugins rewrites the statements to include anIDENTIFIED BY PASSWORDclause, andSET PASSWORDstatements are logged asSET PASSWORDstatements, rather than being rewritten toALTER USERstatements.This variable was added in MySQL 5.7.9. It replaces the
log_backward_compatible_user_definitionsvariable.-
Command-Line Format --log-error[=file_name]System Variable Name log_errorVariable Scope Global Dynamic Variable No Permitted Values Type file nameThe location of the error log, or
stderrif the server is writing error message to the standard error output. See Section 6.4.2, “The Error Log”. -
Introduced 5.7.2 Command-Line Format --log_error_verbosity=#System Variable Name log_error_verbosityVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 3Min Value 1Max Value 3This variable controls verbosity of the server in writing error, warning, and note messages to the error log. The following table shows the permitted values. The default is 3.
Verbosity Value Message Types Logged 1 Errors only 2 Errors and warnings 3 Errors, warnings, and notes log_error_verbositywas added in MySQL 5.7.2. It is preferred over, and should be used instead of, the olderlog_warningssystem variable. See the description oflog_warningsfor information about how that variable relates tolog_error_verbosity. In particular, assigning a value tolog_warningsassigns a value tolog_error_verbosityand vice versa. -
Command-Line Format --log-output=nameSystem Variable Name log_outputVariable Scope Global Dynamic Variable Yes Permitted Values Type setDefault FILEValid Values TABLEFILENONEThe destination for general query log and slow query log output. The value can be a comma-separated list of one or more of the words
TABLE(log to tables),FILE(log to files), orNONE(do not log to tables or files). The default value isFILE.NONE, if present, takes precedence over any other specifiers. If the value isNONElog entries are not written even if the logs are enabled. If the logs are not enabled, no logging occurs even if the value oflog_outputis notNONE. For more information, see Section 6.4.1, “Selecting General Query and Slow Query Log Output Destinations”. -
Command-Line Format --log-queries-not-using-indexesSystem Variable Name log_queries_not_using_indexesVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFWhether queries that do not use indexes are logged to the slow query log. See Section 6.4.5, “The Slow Query Log”.
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Introduced 5.7.5 Command-Line Format --log_syslog[={0|1}]System Variable Name log_syslogVariable Scope Global Dynamic Variable Yes Permitted Values (Unix) Type booleanDefault OFFPermitted Values (Windows) Type booleanDefault ONWhether to write error log output to
syslog(on Unix and Unix-like systems) or Event Log (on Windows). The default value is platform specific:On Unix and Unix-like systems,
syslogoutput is disabled by default.On Windows, Event Log output is enabled by default, which is consistent with older MySQL versions.
Regardless of the default,
log_syslogcan be set explicitly to control output on any supported platform.syslogoutput control is orthogonal to sending error output to a file or (on Windows) to the console. Error output can be directed to the latter destination in addition to or instead ofsyslogas desired. -
Introduced 5.7.5 Command-Line Format --log_syslog_facility=valueSystem Variable Name log_syslog_facilityVariable Scope Global Dynamic Variable Yes Permitted Values Type stringDefault daemonThe facility for error log output written to
syslog(what type of program is sending the message). This variable has no effect unless thelog_syslogsystem variable is enabled.The permitted values can vary per operating system; consult your system
syslogdocumentation.This variable does not exist on Windows.
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Introduced 5.7.5 Command-Line Format --log_syslog_include_pid[={0|1}]System Variable Name log_syslog_include_pidVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault ONWhether to include the server process ID in each line of error log output written to
syslog. This variable has no effect unless thelog_syslogsystem variable is enabled.This variable does not exist on Windows.
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Introduced 5.7.5 Command-Line Format --log_syslog_tag=valueSystem Variable Name log_syslog_tagVariable Scope Global Dynamic Variable Yes Permitted Values Type stringDefault empty stringThe tag to be added to the server identifier in error log output written to
syslog. This variable has no effect unless thelog_syslogsystem variable is enabled.By default, the server identifier is
mysqldwith no tag. If a tag oftag_valis specified, it is appended to the server identifier with a leading hyphen, resulting in an identifier ofmysqld-.tag_valOn Windows, to use a tag that does not already exist, the server must be run from an account with Administrator privileges, to permit creation of a registry entry for the tag. Elevated privileges are not required if the tag already exists.
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Introduced 5.7.2 Command-Line Format --log_timestamps=#System Variable Name log_timestampsVariable Scope Global Dynamic Variable Yes Permitted Values Type enumerationDefault UTCValid Values UTCSYSTEMThis variable controls the timestamp time zone of error log messages, and of general query log and slow query log messages written to files. It does not affect the time zone of general query log and slow query log messages written to tables (
mysql.general_log,mysql.slow_log). Rows retrieved from those tables can be converted from the local system time zone to any desired time zone withCONVERT_TZ()or by setting the sessiontime_zonesystem variable.Permitted
log_timestampsvalues areUTC(the default) andSYSTEM(local system time zone).Timestamps are written using ISO 8601 / RFC 3339 format:
YYYY-MM-DDThh:mm:ss.uuuuuuplus a tail value ofZsignifying Zulu time (UTC) or±hh:mm(an offset from UTC).This variable was added in MySQL 5.7.2. Before 5.7.2, timestamps in log messages were written using the local system time zone by default, not
UTC. If you want the previous log message time zone default, setlog_timestamps=SYSTEM. log_throttle_queries_not_using_indexesSystem Variable Name log_throttle_queries_not_using_indexesVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 0If
log_queries_not_using_indexesis enabled, thelog_throttle_queries_not_using_indexesvariable limits the number of such queries per minute that can be written to the slow query log. A value of 0 (the default) means “no limit”. For more information, see Section 6.4.5, “The Slow Query Log”.-
Introduced 5.7.1 System Variable Name log_slow_admin_statementsVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFInclude slow administrative statements in the statements written to the slow query log. Administrative statements include
ALTER TABLE,ANALYZE TABLE,CHECK TABLE,CREATE INDEX,DROP INDEX,OPTIMIZE TABLE, andREPAIR TABLE. -
Deprecated 5.7.2 Command-Line Format --log-warnings[=#]System Variable Name log_warningsVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms, <= 5.7.1) Type integerDefault 1Min Value 0Max Value 4294967295Permitted Values (32-bit platforms, >= 5.7.2) Type integerDefault 2Min Value 0Max Value 4294967295Permitted Values (64-bit platforms, <= 5.7.1) Type integerDefault 1Min Value 0Max Value 18446744073709551615Permitted Values (64-bit platforms, >= 5.7.2) Type integerDefault 2Min Value 0Max Value 18446744073709551615Whether to produce additional warning messages to the error log. This variable is enabled by default (the default is 1 before MySQL 5.7.2, 2 as of 5.7.2). To disable it, set it to 0. The server logs messages about statements that are unsafe for statement-based logging if the value is greater than 0. Aborted connections and access-denied errors for new connection attempts are logged if the value is greater than 1. See Section B.5.2.11, “Communication Errors and Aborted Connections”.
Enabling this option by setting it greater than 0 is recommended, if you use replication, to get more information about what is happening, such as messages about network failures and reconnections. If the value is greater than 1, aborted connections are written to the error log, and access-denied errors for new connection attempts are written.
If a slave server is started with
log_warningsenabled, the slave prints messages to the error log to provide information about its status, such as the binary log and relay log coordinates where it starts its job, when it is switching to another relay log, when it reconnects after a disconnect, and so forth.As of MySQL 5.7.2, information items previously governed by
log_warningsare governed bylog_error_verbosity, which is preferred over, and should be used instead of, the olderlog_warningssystem variable. (Thelog_warningssystem variable and--log-warningscommand-line option are deprecated and will be removed in a future MySQL release.)Assigning a value to
log_warningsassigns a value tolog_error_verbosityand vice versa. The variables are related as follows:Suppression of all
log_warningsitems, achieved withlog_warnings=0, is achieved withlog_error_verbosity=1(errors only).Items printed for
log_warnings=1or higher count as warnings and are printed forlog_error_verbosity=2or higher.Items printed for
log_warnings=2count as notes and are printed forlog_error_verbosity=3.
As of MySQL 5.7.2, the default log level is controlled by
log_error_verbosity, which has a default of 3. In addition, the default forlog_warningschanges from 1 to 2, which corresponds tolog_error_verbosity=3. To achieve a logging level similar to the previous default, setlog_error_verbosity=2.In MySQL 5.7.2 and higher, use of
log_warningsis still permitted but maps onto use oflog_error_verbosityas follows:Setting
log_warnings=0is equivalent tolog_error_verbosity=1(errors only).Setting
log_warnings=1is equivalent tolog_error_verbosity=2(errors, warnings).Setting
log_warnings=2(or higher) is equivalent tolog_error_verbosity=3(errors, warnings, notes), and the server setslog_warningsto 2 if a larger value is specified.
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Command-Line Format --long_query_time=#System Variable Name long_query_timeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type numericDefault 10Min Value 0If a query takes longer than this many seconds, the server increments the
Slow_queriesstatus variable. If the slow query log is enabled, the query is logged to the slow query log file. This value is measured in real time, not CPU time, so a query that is under the threshold on a lightly loaded system might be above the threshold on a heavily loaded one. The minimum and default values oflong_query_timeare 0 and 10, respectively. The value can be specified to a resolution of microseconds. For logging to a file, times are written including the microseconds part. For logging to tables, only integer times are written; the microseconds part is ignored. See Section 6.4.5, “The Slow Query Log”. -
Command-Line Format --low-priority-updatesSystem Variable Name low_priority_updatesVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault FALSEIf set to
1, allINSERT,UPDATE,DELETE, andLOCK TABLE WRITEstatements wait until there is no pendingSELECTorLOCK TABLE READon the affected table. This affects only storage engines that use only table-level locking (such asMyISAM,MEMORY, andMERGE). -
System Variable Name lower_case_file_systemVariable Scope Global Dynamic Variable No Permitted Values Type booleanThis variable describes the case sensitivity of file names on the file system where the data directory is located.
OFFmeans file names are case sensitive,ONmeans they are not case sensitive. This variable is read only because it reflects a file system attribute and setting it would have no effect on the file system. -
Command-Line Format --lower_case_table_names[=#]System Variable Name lower_case_table_namesVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 0Min Value 0Max Value 2If set to 0, table names are stored as specified and comparisons are case sensitive. If set to 1, table names are stored in lowercase on disk and comparisons are not case sensitive. If set to 2, table names are stored as given but compared in lowercase. This option also applies to database names and table aliases. For additional information, see Section 10.2.2, “Identifier Case Sensitivity”.
On Windows the default value is 1. On OS X, the default value is 2.
You should not set
lower_case_table_namesto 0 if you are running MySQL on a system where the data directory resides on a case-insensitive file system (such as on Windows or OS X). It is an unsupported combination that could result in a hang condition when running anINSERT INTO ... SELECT ... FROMoperation with the wrongtbl_nametbl_nameletter case. WithMyISAM, accessing table names using different letter cases could cause index corruption.As of MySQL 5.7.9, an error message is printed and the server exits if you attempt to start the server with
--lower_case_table_names=0on a case-insensitive file system.If you are using
InnoDBtables, you should set this variable to 1 on all platforms to force names to be converted to lowercase.The setting of this variable in MySQL 5.7 affects the behavior of replication filtering options with regard to case sensitivity. (Bug #51639) See Section 18.2.5, “How Servers Evaluate Replication Filtering Rules”, for more information.
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Command-Line Format --max_allowed_packet=#System Variable Name max_allowed_packetVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 4194304Min Value 1024Max Value 1073741824The maximum size of one packet or any generated/intermediate string, or any parameter sent by the
mysql_stmt_send_long_data()C API function. The default is 4MB.The packet message buffer is initialized to
net_buffer_lengthbytes, but can grow up tomax_allowed_packetbytes when needed. This value by default is small, to catch large (possibly incorrect) packets.You must increase this value if you are using large
BLOBcolumns or long strings. It should be as big as the largestBLOByou want to use. The protocol limit formax_allowed_packetis 1GB. The value should be a multiple of 1024; nonmultiples are rounded down to the nearest multiple.When you change the message buffer size by changing the value of the
max_allowed_packetvariable, you should also change the buffer size on the client side if your client program permits it. The defaultmax_allowed_packetvalue built in to the client library is 1GB, but individual client programs might override this. For example, mysql and mysqldump have defaults of 16MB and 24MB, respectively. They also enable you to change the client-side value by settingmax_allowed_packeton the command line or in an option file.The session value of this variable is read only. The client can receive up to as many bytes as the session value. However, the server will not send to the client more bytes than the current global
max_allowed_packetvalue. (The global value could be less than the session value if the global value is changed after the client connects.) -
Command-Line Format --max_connect_errors=#System Variable Name max_connect_errorsVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 100Min Value 1Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 100Min Value 1Max Value 18446744073709551615If more than this many successive connection requests from a host are interrupted without a successful connection, the server blocks that host from further connections. You can unblock blocked hosts by flushing the host cache. To do so, issue a
FLUSH HOSTSstatement or execute a mysqladmin flush-hosts command. If a connection is established successfully within fewer thanmax_connect_errorsattempts after a previous connection was interrupted, the error count for the host is cleared to zero. However, once a host is blocked, flushing the host cache is the only way to unblock it. The default is 100. -
Command-Line Format --max_connections=#System Variable Name max_connectionsVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 151Min Value 1Max Value 100000The maximum permitted number of simultaneous client connections. By default, this is 151. See Section B.5.2.7, “Too many connections”, for more information.
Increasing this value increases the number of file descriptors that mysqld requires. If the required number of descriptors are not available, the server reduces the value of
max_connections. See Section 9.4.3.1, “How MySQL Opens and Closes Tables”, for comments on file descriptor limits.Connections refused because the
max_connectionslimit is reached increment theConnection_errors_max_connectionsstatus variable. -
Deprecated 5.6.7 Command-Line Format --max_delayed_threads=#System Variable Name max_delayed_threadsVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 20Min Value 0Max Value 16384This system variable is deprecated (because
DELAYEDinserts are not supported), and will be removed in a future release. -
Introduced 5.7.6 Command-Line Format --max_digest_length=#System Variable Name max_digest_lengthVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 1024Min Value 0Max Value 1048576The maximum number of bytes available for computing statement digests (see Section 23.7, “Performance Schema Statement Digests”). When this amount of space is used for computing the digest for a statement, no further tokens from the parsed statement are collected or figure into the digest value. Statements differing only after that many bytes of parsed statement tokens produce the same digest and are aggregated for digest statistics.
Decreasing the
max_digest_lengthvalue reduces memory use but causes the digest value of more statements to become indistinguishable if they differ only at the end. Increasing the value permits longer statements to be distinguished but increases memory use, particularly for workloads that involve large numbers of simultaneous sessions (max_digest_lengthbytes are allocated per session).This variable was added in MySQL 5.7.6. Until 5.7.8, this variable applies to Performance Schema and to other server functions that use digests, such as query rewrite plugins. As of 5.7.8, it no longer applies to Performance Schema; instead, use
performance_schema_max_digest_length. -
Command-Line Format --max_error_count=#System Variable Name max_error_countVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 64Min Value 0Max Value 65535The maximum number of error, warning, and note messages to be stored for display by the
SHOW ERRORSandSHOW WARNINGSstatements. This is the same as the number of condition areas in the diagnostics area, and thus the number of conditions that can be inspected byGET DIAGNOSTICS. -
Introduced 5.7.8 Command-Line Format --max_execution_time=#System Variable Name max_execution_timeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 0The execution timeout for
SELECTstatements, in milliseconds. If the value is 0, timeouts are not enabled.max_execution_timeapplies as follows:The global
max_execution_timevalue provides the default for the session value for new connections. The session value applies toSELECTexecutions executed within the session that include noMAX_EXECUTION_TIME(optimizer hint or for whichN)Nis 0.max_execution_timeapplies to read-onlySELECTstatements. Statements that are not read only are those that invoke a stored function that modifies data as a side effect.max_execution_timeis ignored forSELECTstatements in stored programs.
This variable was added in MySQL 5.7.8. Previously, it was named
max_statement_time. -
Command-Line Format --max_heap_table_size=#System Variable Name max_heap_table_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 16777216Min Value 16384Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 16777216Min Value 16384Max Value 1844674407370954752This variable sets the maximum size to which user-created
MEMORYtables are permitted to grow. The value of the variable is used to calculateMEMORYtableMAX_ROWSvalues. Setting this variable has no effect on any existingMEMORYtable, unless the table is re-created with a statement such asCREATE TABLEor altered withALTER TABLEorTRUNCATE TABLE. A server restart also sets the maximum size of existingMEMORYtables to the globalmax_heap_table_sizevalue.This variable is also used in conjunction with
tmp_table_sizeto limit the size of internal in-memory tables. See Section 9.4.4, “Internal Temporary Table Use in MySQL”.max_heap_table_sizeis not replicated. See Section 18.4.1.23, “Replication and MEMORY Tables”, and Section 18.4.1.38, “Replication and Variables”, for more information. -
Deprecated 5.6.7 System Variable Name max_insert_delayed_threadsVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerThis variable is a synonym for
max_delayed_threads.This system variable is deprecated (because
DELAYEDinserts are not supported), and will be removed in a future release. -
Command-Line Format --max_join_size=#System Variable Name max_join_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 18446744073709551615Min Value 1Max Value 18446744073709551615Do not permit statements that probably need to examine more than
max_join_sizerows (for single-table statements) or row combinations (for multiple-table statements) or that are likely to do more thanmax_join_sizedisk seeks. By setting this value, you can catch statements where keys are not used properly and that would probably take a long time. Set it if your users tend to perform joins that lack aWHEREclause, that take a long time, or that return millions of rows.Setting this variable to a value other than
DEFAULTresets the value ofsql_big_selectsto0. If you set thesql_big_selectsvalue again, themax_join_sizevariable is ignored.If a query result is in the query cache, no result size check is performed, because the result has previously been computed and it does not burden the server to send it to the client.
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Command-Line Format --max_length_for_sort_data=#System Variable Name max_length_for_sort_dataVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 1024Min Value 4Max Value 8388608The cutoff on the size of index values that determines which
filesortalgorithm to use. See Section 9.2.1.15, “ORDER BY Optimization”. -
Introduced 5.7.8 Command-Line Format --max_points_in_geometry=integerSystem Variable Name max_points_in_geometryVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 65536Min Value 3Max Value 1048576The maximum value of the
points_per_circleargument to theST_Buffer_Strategy()function. -
Command-Line Format --max_prepared_stmt_count=#System Variable Name max_prepared_stmt_countVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 16382Min Value 0Max Value 1048576This variable limits the total number of prepared statements in the server. It can be used in environments where there is the potential for denial-of-service attacks based on running the server out of memory by preparing huge numbers of statements. If the value is set lower than the current number of prepared statements, existing statements are not affected and can be used, but no new statements can be prepared until the current number drops below the limit. The default value is 16,382. The permissible range of values is from 0 to 1 million. Setting the value to 0 disables prepared statements.
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Command-Line Format --max_relay_log_size=#System Variable Name max_relay_log_sizeVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 0Min Value 0Max Value 1073741824If a write by a replication slave to its relay log causes the current log file size to exceed the value of this variable, the slave rotates the relay logs (closes the current file and opens the next one). If
max_relay_log_sizeis 0, the server usesmax_binlog_sizefor both the binary log and the relay log. Ifmax_relay_log_sizeis greater than 0, it constrains the size of the relay log, which enables you to have different sizes for the two logs. You must setmax_relay_log_sizeto between 4096 bytes and 1GB (inclusive), or to 0. The default value is 0. See Section 18.2.2, “Replication Implementation Details”. -
Command-Line Format --max_seeks_for_key=#System Variable Name max_seeks_for_keyVariable Scope Global, Session Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 4294967295Min Value 1Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 18446744073709551615Min Value 1Max Value 18446744073709551615Limit the assumed maximum number of seeks when looking up rows based on a key. The MySQL optimizer assumes that no more than this number of key seeks are required when searching for matching rows in a table by scanning an index, regardless of the actual cardinality of the index (see Section 14.7.5.22, “SHOW INDEX Syntax”). By setting this to a low value (say, 100), you can force MySQL to prefer indexes instead of table scans.
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Command-Line Format --max_sort_length=#System Variable Name max_sort_lengthVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 1024Min Value 4Max Value 8388608The number of bytes to use when sorting data values. The server uses only the first
max_sort_lengthbytes of each value and ignores the rest. Consequently, values that differ only after the firstmax_sort_lengthbytes compare as equal forGROUP BY,ORDER BY, andDISTINCToperations.Increasing the value of
max_sort_lengthmay require increasing the value ofsort_buffer_sizeas well. For details, see Section 9.2.1.15, “ORDER BY Optimization” -
Command-Line Format --max_sp_recursion_depth[=#]System Variable Name max_sp_recursion_depthVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 0Max Value 255The number of times that any given stored procedure may be called recursively. The default value for this option is 0, which completely disables recursion in stored procedures. The maximum value is 255.
Stored procedure recursion increases the demand on thread stack space. If you increase the value of
max_sp_recursion_depth, it may be necessary to increase thread stack size by increasing the value ofthread_stackat server startup. -
Introduced 5.7.4 Removed 5.7.8 System Variable Name max_statement_timeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 0The execution timeout for
SELECTstatements, in milliseconds. If the value is 0, timeouts are not enabled.max_statement_timeapplies as follows:The global
max_statement_timevalue provides the default for the session value for new connections. The session value applies toSELECTstatements executed within the session that include noMAX_STATEMENT_TIME =option or for whichNNis 0.max_statement_timeapplies to read-onlySELECTstatements. Statements that are not read only are those that invoke a stored function that modifies data as a side effect.max_statement_timeis ignored forSELECTstatements in stored programs.
This variable was added in MySQL 5.7.4 and renamed to
max_execution_timein MySQL 5.7.8. This variable is unused. It is deprecated and will be removed in a future MySQL release.
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Command-Line Format --max_user_connections=#System Variable Name max_user_connectionsVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 0Min Value 0Max Value 4294967295The maximum number of simultaneous connections permitted to any given MySQL user account. A value of 0 (the default) means “no limit.”
This variable has a global value that can be set at server startup or runtime. It also has a read-only session value that indicates the effective simultaneous-connection limit that applies to the account associated with the current session. The session value is initialized as follows:
If the user account has a nonzero
MAX_USER_CONNECTIONSresource limit, the sessionmax_user_connectionsvalue is set to that limit.Otherwise, the session
max_user_connectionsvalue is set to the global value.
Account resource limits are specified using the
CREATE USERorALTER USERstatement. See Section 7.3.4, “Setting Account Resource Limits”. -
Command-Line Format --max_write_lock_count=#System Variable Name max_write_lock_countVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 4294967295Min Value 1Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 18446744073709551615Min Value 1Max Value 18446744073709551615After this many write locks, permit some pending read lock requests to be processed in between.
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Introduced 5.7.6 Command-Line Format --mecab_rc_fileSystem Variable Name mecab_rc_fileVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe
mecab_rc_fileoption is used when setting up the MeCab full-text parser.The
mecab_rc_fileoption defines the path to themecabrcconfiguration file, which is the configuration file for MeCab. The option is read-only and can only be set at startup. Themecabrcconfiguration file is required to initialize MeCab.For information about the MeCab full-text parser, see Section 13.9.9, “MeCab Full-Text Parser Plugin”.
For information about options that can be specified in the MeCab
mecabrcconfiguration file, refer to the MeCab Documentation on the Google Developers site. -
Deprecated 5.7.4 System Variable Name metadata_locks_cache_sizeVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 1024Min Value 1Max Value 1048576The size of the metadata locks cache. The server uses this cache to avoid creation and destruction of synchronization objects. This is particularly helpful on systems where such operations are expensive, such as Windows XP.
In MySQL 5.7.4, metadata locking implementation changes make this variable unnecessary, so it is deprecated and will be removed in a future MySQL release.
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Deprecated 5.7.4 System Variable Name metadata_locks_hash_instancesVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 8Min Value 1Max Value 1024The set of metadata locks can be partitioned into separate hashes to permit connections accessing different objects to use different locking hashes and reduce contention. The
metadata_locks_hash_instancessystem variable specifies the number of hashes (default 8).In MySQL 5.7.4, metadata locking implementation changes make this variable unnecessary, so it is deprecated and will be removed in a future MySQL release.
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Command-Line Format --min-examined-row-limit=#System Variable Name min_examined_row_limitVariable Scope Global, Session Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 0Min Value 0Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 0Min Value 0Max Value 18446744073709551615Queries that examine fewer than this number of rows are not logged to the slow query log.
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Deprecated 5.6.7 Command-Line Format --multi_range_count=#System Variable Name multi_range_countVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 256Min Value 1Max Value 4294967295This variable has no effect. It is deprecated and will be removed in a future MySQL release.
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Command-Line Format --myisam_data_pointer_size=#System Variable Name myisam_data_pointer_sizeVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 6Min Value 2Max Value 7The default pointer size in bytes, to be used by
CREATE TABLEforMyISAMtables when noMAX_ROWSoption is specified. This variable cannot be less than 2 or larger than 7. The default value is 6. See Section B.5.2.12, “The table is full”. -
Command-Line Format --myisam_max_sort_file_size=#System Variable Name myisam_max_sort_file_sizeVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 2147483648Permitted Values (64-bit platforms) Type integerDefault 9223372036854775807The maximum size of the temporary file that MySQL is permitted to use while re-creating a
MyISAMindex (duringREPAIR TABLE,ALTER TABLE, orLOAD DATA INFILE). If the file size would be larger than this value, the index is created using the key cache instead, which is slower. The value is given in bytes.If
MyISAMindex files exceed this size and disk space is available, increasing the value may help performance. The space must be available in the file system containing the directory where the original index file is located. -
Command-Line Format --myisam_mmap_size=#System Variable Name myisam_mmap_sizeVariable Scope Global Dynamic Variable No Permitted Values (32-bit platforms) Type integerDefault 4294967295Min Value 7Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 18446744073709551615Min Value 7Max Value 18446744073709551615The maximum amount of memory to use for memory mapping compressed
MyISAMfiles. If many compressedMyISAMtables are used, the value can be decreased to reduce the likelihood of memory-swapping problems. -
System Variable Name myisam_recover_optionsVariable Scope Global Dynamic Variable No The value of the
--myisam-recover-optionsoption. See Section 6.1.3, “Server Command Options”. -
Command-Line Format --myisam_repair_threads=#System Variable Name myisam_repair_threadsVariable Scope Global, Session Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 1Min Value 1Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 1Min Value 1Max Value 18446744073709551615If this value is greater than 1,
MyISAMtable indexes are created in parallel (each index in its own thread) during theRepair by sortingprocess. The default value is 1.NoteMulti-threaded repair is still beta-quality code.
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Command-Line Format --myisam_sort_buffer_size=#System Variable Name myisam_sort_buffer_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (Windows, 32-bit platforms) Type integerDefault 8388608Min Value 4096Max Value 4294967295Permitted Values (Windows, 64-bit platforms) Type integerDefault 8388608Min Value 4096Max Value 18446744073709551615Permitted Values (Other, 32-bit platforms) Type integerDefault 8388608Min Value 4096Max Value 4294967295Permitted Values (Other, 64-bit platforms) Type integerDefault 8388608Min Value 4096Max Value 18446744073709551615The size of the buffer that is allocated when sorting
MyISAMindexes during aREPAIR TABLEor when creating indexes withCREATE INDEXorALTER TABLE.The maximum permissible setting for
myisam_sort_buffer_sizeis 4GB−1. Larger values are permitted for 64-bit platforms. -
Command-Line Format --myisam_stats_method=nameSystem Variable Name myisam_stats_methodVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type enumerationDefault nulls_unequalValid Values nulls_equalnulls_unequalnulls_ignoredHow the server treats
NULLvalues when collecting statistics about the distribution of index values forMyISAMtables. This variable has three possible values,nulls_equal,nulls_unequal, andnulls_ignored. Fornulls_equal, allNULLindex values are considered equal and form a single value group that has a size equal to the number ofNULLvalues. Fornulls_unequal,NULLvalues are considered unequal, and eachNULLforms a distinct value group of size 1. Fornulls_ignored,NULLvalues are ignored.The method that is used for generating table statistics influences how the optimizer chooses indexes for query execution, as described in Section 9.3.7, “InnoDB and MyISAM Index Statistics Collection”.
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Command-Line Format --myisam_use_mmapSystem Variable Name myisam_use_mmapVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFUse memory mapping for reading and writing
MyISAMtables. mysql_native_password_proxy_usersIntroduced 5.7.7 Command-Line Format --mysql_native_password_proxy_users=[={OFF|ON}]System Variable Name mysql_native_password_proxy_usersVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFThis variable controls whether the
mysql_native_passwordbuilt-in authentication plugin supports proxy users. It has no effect unless thecheck_proxy_userssystem variable is enabled. For information about user proxying, see Section 7.3.9, “Proxy Users”.This variable was added in MySQL 5.7.7. Before 5.7.7,
mysql_native_passworddoes not support proxy users.-
System Variable Name named_pipeVariable Scope Global Dynamic Variable No Platform Specific Windows Permitted Values (Windows) Type booleanDefault OFF(Windows only.) Indicates whether the server supports connections over named pipes.
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Command-Line Format --net_buffer_length=#System Variable Name net_buffer_lengthVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 16384Min Value 1024Max Value 1048576Each client thread is associated with a connection buffer and result buffer. Both begin with a size given by
net_buffer_lengthbut are dynamically enlarged up tomax_allowed_packetbytes as needed. The result buffer shrinks tonet_buffer_lengthafter each SQL statement.This variable should not normally be changed, but if you have very little memory, you can set it to the expected length of statements sent by clients. If statements exceed this length, the connection buffer is automatically enlarged. The maximum value to which
net_buffer_lengthcan be set is 1MB.The session value of this variable is read only.
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Command-Line Format --net_read_timeout=#System Variable Name net_read_timeoutVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 30Min Value 1The number of seconds to wait for more data from a connection before aborting the read. When the server is reading from the client,
net_read_timeoutis the timeout value controlling when to abort. When the server is writing to the client,net_write_timeoutis the timeout value controlling when to abort. See alsoslave_net_timeout. -
Command-Line Format --net_retry_count=#System Variable Name net_retry_countVariable Scope Global, Session Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 10Min Value 1Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 10Min Value 1Max Value 18446744073709551615If a read or write on a communication port is interrupted, retry this many times before giving up. This value should be set quite high on FreeBSD because internal interrupts are sent to all threads.
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Command-Line Format --net_write_timeout=#System Variable Name net_write_timeoutVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 60Min Value 1The number of seconds to wait for a block to be written to a connection before aborting the write. See also
net_read_timeout. -
Command-Line Format --newSystem Variable Name newVariable Scope Global, Session Dynamic Variable Yes Disabled by skip-newPermitted Values Type booleanDefault FALSEThis variable was used in MySQL 4.0 to turn on some 4.1 behaviors, and is retained for backward compatibility. Its value is always
OFF.In MySQL Cluster, setting this variable to
ONmakes it possible to employ partitioning types other thanKEYorLINEAR KEYwithNDBtables. This feature is experimental only, and not supported in production. For additional information, see User-defined partitioning and the NDB storage engine (MySQL Cluster). -
Introduced 5.7.6 Command-Line Format --ngram_token_sizeSystem Variable Name ngram_token_sizeVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 2Min Value 1Max Value 10Defines the n-gram token size for the n-gram full-text parser. The
ngram_token_sizeoption is read-only and can only be modified at startup. The default value is 2 (bigram). The maximum value is 10.For more information about how to configure this variable, see Section 13.9.8, “ngram Full-Text Parser”.
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Introduced 5.7.5 Command-Line Format --offline_mode=valSystem Variable Name offline_modeVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFWhether the server is in “offline mode”, which has these characteristics:
Connected client users who do not have the
SUPERprivilege are disconnected on the next request, with an appropriate error. Disconnection includes terminating running statements and releasing locks. Such clients also cannot initiate new connections, and receive an appropriate error.Connected client users who have the
SUPERprivilege are not disconnected, and can initiate new connections to manage the server.Replication slave threads are permitted to keep applying data to the server.
Only users who have the
SUPERprivilege can control offline mode. To put a server in offline mode, change the value of theoffline_modesystem variable fromOFFtoON. To resume normal operations, changeoffline_modefromONtoOFF. In offline mode, clients that are refused access receive anER_SERVER_OFFLINE_MODEerror. -
Command-Line Format --oldSystem Variable Name oldVariable Scope Global Dynamic Variable No oldis a compatibility variable. It is disabled by default, but can be enabled at startup to revert the server to behaviors present in older versions.When
oldis enabled, it changes the default scope of index hints to that used prior to MySQL 5.1.17. That is, index hints with noFORclause apply only to how indexes are used for row retrieval and not to resolution ofORDER BYorGROUP BYclauses. (See Section 9.9.4, “Index Hints”.) Take care about enabling this in a replication setup. With statement-based binary logging, having different modes for the master and slaves might lead to replication errors. -
Command-Line Format --old-alter-tableSystem Variable Name old_alter_tableVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault OFFWhen this variable is enabled, the server does not use the optimized method of processing an
ALTER TABLEoperation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation ofALTER TABLE, see Section 14.1.8, “ALTER TABLE Syntax”. -
Deprecated 5.7.6 System Variable Name old_passwordsVariable Scope Global, Session Dynamic Variable Yes Permitted Values (<= 5.7.4) Type enumerationDefault 0Valid Values 012Permitted Values (>= 5.7.5) Type enumerationDefault 0Valid Values 02NoteThis system variable is deprecated as of MySQL 5.7.6 and will be removed in a future MySQL release.
This variable controls the password hashing method used by the
PASSWORD()function. It also influences password hashing performed byCREATE USERandGRANTstatements that specify a password using anIDENTIFIED BYclause.The following table shows the permitted values of
old_passwords, the password hashing method for each value, and which authentication plugins use passwords hashed with each method.Value Password Hashing Method Associated Authentication Plugin 0 MySQL 4.1 native hashing mysql_native_password1 Pre-4.1 (“old”) hashing mysql_old_password2 SHA-256 hashing sha256_passwordNotePasswords that use the pre-4.1 hashing method are less secure than passwords that use the native password hashing method and should be avoided. Pre-4.1 passwords are deprecated and support for them is removed in MySQL 5.7.5. Consequently,
old_passwords=1, which causesPASSWORD()to generate pre-4.1 password hashes, is not permitted as of 5.7.5. For account upgrade instructions, see Section 7.5.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.If
old_passwords=1,PASSWORD(returns the same value asstr)OLD_PASSWORD(. The latter function is not affected by the value ofstr)old_passwords.If you set
old_passwords=2, follow the instructions for using thesha256_passwordplugin at Section 7.5.1.4, “The SHA-256 Authentication Plugin”.The server sets the global
old_passwordsvalue during startup to be consistent with the password hashing method required by the default authentication plugin. The default plugin ismysql_native_passwordunless thedefault_authentication_pluginsystem variable is set otherwise.As of MySQL 5.7.1, when a client successfully connects to the server, the server sets the session
old_passwordsvalue appropriately for the account authentication method. For example, if the account uses thesha256_passwordauthentication plugin, the server setsold_passwords=2.For additional information about authentication plugins and hashing formats, see Section 7.3.8, “Pluggable Authentication”, and Section 7.1.2.4, “Password Hashing in MySQL”.
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Command-Line Format --open-files-limit=#System Variable Name open_files_limitVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 5000, with possible adjustmentMin Value 0Max Value platform dependentThe number of files that the operating system permits mysqld to open. The value of this variable at runtime is the real value permitted by the system and might be different from the value you specify at server startup. The value is 0 on systems where MySQL cannot change the number of open files.
The effective
open_files_limitvalue is based on the value specified at system startup (if any) and the values ofmax_connectionsandtable_open_cache, using these formulas:1) 10 + max_connections + (table_open_cache * 2) 2) max_connections * 5 3) open_files_limit value specified at startup, 5000 if none
The server attempts to obtain the number of file descriptors using the maximum of those three values. If that many descriptors cannot be obtained, the server attempts to obtain as many as the system will permit.
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Command-Line Format --optimizer_prune_level[=#]System Variable Name optimizer_prune_levelVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault 1Controls the heuristics applied during query optimization to prune less-promising partial plans from the optimizer search space. A value of 0 disables heuristics so that the optimizer performs an exhaustive search. A value of 1 causes the optimizer to prune plans based on the number of rows retrieved by intermediate plans.
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Command-Line Format --optimizer_search_depth[=#]System Variable Name optimizer_search_depthVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 62Min Value 0Max Value 62The maximum depth of search performed by the query optimizer. Values larger than the number of relations in a query result in better query plans, but take longer to generate an execution plan for a query. Values smaller than the number of relations in a query return an execution plan quicker, but the resulting plan may be far from being optimal. If set to 0, the system automatically picks a reasonable value.
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Command-Line Format --optimizer_switch=valueSystem Variable Name optimizer_switchVariable Scope Global, Session Dynamic Variable Yes Permitted Values (<= 5.7.4) Type setValid Values batched_key_access={on|off}block_nested_loop={on|off}engine_condition_pushdown={on|off}firstmatch={on|off}index_condition_pushdown={on|off}index_merge={on|off}index_merge_intersection={on|off}index_merge_sort_union={on|off}index_merge_union={on|off}loosescan={on|off}materialization={on|off}mrr={on|off}mrr_cost_based={on|off}semijoin={on|off}subquery_materialization_cost_based={on|off}use_index_extensions={on|off}Permitted Values (5.7.5) Type setValid Values batched_key_access={on|off}block_nested_loop={on|off}condition_fanout_filter={on|off}engine_condition_pushdown={on|off}firstmatch={on|off}index_condition_pushdown={on|off}index_merge={on|off}index_merge_intersection={on|off}index_merge_sort_union={on|off}index_merge_union={on|off}loosescan={on|off}materialization={on|off}mrr={on|off}mrr_cost_based={on|off}semijoin={on|off}subquery_materialization_cost_based={on|off}use_index_extensions={on|off}Permitted Values (>= 5.7.6, <= 5.7.7) Type setValid Values batched_key_access={on|off}block_nested_loop={on|off}condition_fanout_filter={on|off}derived_merge={on|off}engine_condition_pushdown={on|off}firstmatch={on|off}index_condition_pushdown={on|off}index_merge={on|off}index_merge_intersection={on|off}index_merge_sort_union={on|off}index_merge_union={on|off}loosescan={on|off}materialization={on|off}mrr={on|off}mrr_cost_based={on|off}semijoin={on|off}subquery_materialization_cost_based={on|off}use_index_extensions={on|off}Permitted Values (>= 5.7.8) Type setValid Values batched_key_access={on|off}block_nested_loop={on|off}condition_fanout_filter={on|off}derived_merge={on|off}duplicateweedout={on|off}engine_condition_pushdown={on|off}firstmatch={on|off}index_condition_pushdown={on|off}index_merge={on|off}index_merge_intersection={on|off}index_merge_sort_union={on|off}index_merge_union={on|off}loosescan={on|off}materialization={on|off}mrr={on|off}mrr_cost_based={on|off}semijoin={on|off}subquery_materialization_cost_based={on|off}use_index_extensions={on|off}The
optimizer_switchsystem variable enables control over optimizer behavior. The value of this variable is a set of flags, each of which has a value ofonoroffto indicate whether the corresponding optimizer behavior is enabled or disabled. This variable has global and session values and can be changed at runtime. The global default can be set at server startup.To see the current set of optimizer flags, select the variable value:
mysql>
SELECT @@optimizer_switch\G*************************** 1. row *************************** @@optimizer_switch: index_merge=on,index_merge_union=on, index_merge_sort_union=on, index_merge_intersection=on, engine_condition_pushdown=on, index_condition_pushdown=on, mrr=on,mrr_cost_based=on, block_nested_loop=on,batched_key_access=off, materialization=on,semijoin=on,loosescan=on, firstmatch=on,duplicateweedout=on, subquery_materialization_cost_based=on, use_index_extensions=on, condition_fanout_filter=on,derived_merge=onFor more information about the syntax of this variable and the optimizer behaviors that it controls, see Section 9.9.2, “Controlling Switchable Optimizations”.
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System Variable Name optimizer_traceVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringThis variable controls optimizer tracing. For details, see MySQL Internals: Tracing the Optimizer.
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System Variable Name optimizer_trace_featuresVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringThis variable enables or disables selected optimizer tracing features. For details, see MySQL Internals: Tracing the Optimizer.
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System Variable Name optimizer_trace_limitVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 1The maximum number of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.
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System Variable Name optimizer_trace_max_mem_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 16384The maximum cumulative size of stored optimizer traces. For details, see MySQL Internals: Tracing the Optimizer.
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System Variable Name optimizer_trace_offsetVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault -1The offset of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.
performance_schema_xxxPerformance Schema system variables are listed in Section 23.12, “Performance Schema System Variables”. These variables may be used to configure Performance Schema operation.
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Introduced 5.7.12 Command-Line Format --parser_max_mem_size=NSystem Variable Name parser_max_mem_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 4294967295Min Value 400000Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 18446744073709551615Min Value 400000Max Value 18446744073709551615The maximum amount of memory available to the parser. The default value places no limit on memory available. The value can be reduced to protect against out-of-memory situations caused by parsing long or complex SQL statements.
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Command-Line Format --pid-file=file_nameSystem Variable Name pid_fileVariable Scope Global Dynamic Variable No Permitted Values Type file nameThe path name of the process ID (PID) file. This variable can be set with the
--pid-fileoption. -
Command-Line Format --plugin_dir=dir_nameSystem Variable Name plugin_dirVariable Scope Global Dynamic Variable No Permitted Values Type directory nameDefault BASEDIR/lib/pluginThe path name of the plugin directory.
If the plugin directory is writable by the server, it may be possible for a user to write executable code to a file in the directory using
SELECT ... INTO DUMPFILE. This can be prevented by makingplugin_dirread only to the server or by setting--secure-file-privto a directory whereSELECTwrites can be made safely. -
Command-Line Format --port=#System Variable Name portVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 3306Min Value 0Max Value 65535The number of the port on which the server listens for TCP/IP connections. This variable can be set with the
--portoption. -
Command-Line Format --preload_buffer_size=#System Variable Name preload_buffer_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 32768Min Value 1024Max Value 1073741824The size of the buffer that is allocated when preloading indexes.
If set to 0 or
OFF(the default), statement profiling is disabled. If set to 1 orON, statement profiling is enabled and theSHOW PROFILEandSHOW PROFILESstatements provide access to profiling information. See Section 14.7.5.31, “SHOW PROFILES Syntax”.This variable is deprecated and will be removed in a future MySQL release.
The number of statements for which to maintain profiling information if
profilingis enabled. The default value is 15. The maximum value is 100. Setting the value to 0 effectively disables profiling. See Section 14.7.5.31, “SHOW PROFILES Syntax”.This variable is deprecated and will be removed in a future MySQL release.
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System Variable Name protocol_versionVariable Scope Global Dynamic Variable No Permitted Values Type integerThe version of the client/server protocol used by the MySQL server.
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System Variable Name proxy_userVariable Scope Session Dynamic Variable No Permitted Values Type stringIf the current client is a proxy for another user, this variable is the proxy user account name. Otherwise, this variable is
NULL. See Section 7.3.9, “Proxy Users”. -
System Variable Name pseudo_slave_modeVariable Scope Session Dynamic Variable Yes Permitted Values Type integerThis variable is for internal server use.
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System Variable Name pseudo_thread_idVariable Scope Session Dynamic Variable Yes Permitted Values Type integerThis variable is for internal server use.
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Command-Line Format --query_alloc_block_size=#System Variable Name query_alloc_block_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (>= 5.7.9) Type integerDefault 8192Min Value 1024Max Value 4294967295Block Size 1024Permitted Values (32-bit platforms, <= 5.7.8) Type integerDefault 8192Min Value 1024Max Value 4294967295Block Size 1024Permitted Values (64-bit platforms, <= 5.7.8) Type integerDefault 8192Min Value 1024Max Value 18446744073709551615Block Size 1024The allocation size of memory blocks that are allocated for objects created during statement parsing and execution. If you have problems with memory fragmentation, it might help to increase this parameter.
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Command-Line Format --query_cache_limit=#System Variable Name query_cache_limitVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 1048576Min Value 0Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 1048576Min Value 0Max Value 18446744073709551615Do not cache results that are larger than this number of bytes. The default value is 1MB.
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Command-Line Format --query_cache_min_res_unit=#System Variable Name query_cache_min_res_unitVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 4096Min Value 512Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 4096Min Value 512Max Value 18446744073709551615The minimum size (in bytes) for blocks allocated by the query cache. The default value is 4096 (4KB). Tuning information for this variable is given in Section 9.10.3.3, “Query Cache Configuration”.
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Command-Line Format --query_cache_size=#System Variable Name query_cache_sizeVariable Scope Global Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 1048576Min Value 0Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 1048576Min Value 0Max Value 18446744073709551615The amount of memory allocated for caching query results. By default, the query cache is disabled. This is achieved using a default value of 1M, with a default for
query_cache_typeof 0. (To reduce overhead significantly if you set the size to 0, you should also start the server withquery_cache_type=0.The permissible values are multiples of 1024; other values are rounded down to the nearest multiple.
query_cache_sizebytes of memory are allocated even ifquery_cache_typeis set to 0. See Section 9.10.3.3, “Query Cache Configuration”, for more information.The query cache needs a minimum size of about 40KB to allocate its structures. (The exact size depends on system architecture.) If you set the value of
query_cache_sizetoo small, a warning will occur, as described in Section 9.10.3.3, “Query Cache Configuration”. -
Command-Line Format --query_cache_type=#System Variable Name query_cache_typeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type enumerationDefault 0Valid Values 012Set the query cache type. Setting the
GLOBALvalue sets the type for all clients that connect thereafter. Individual clients can set theSESSIONvalue to affect their own use of the query cache. Possible values are shown in the following table.Option Description 0orOFFDo not cache results in or retrieve results from the query cache. Note that this does not deallocate the query cache buffer. To do that, you should set query_cache_sizeto 0.1orONCache all cacheable query results except for those that begin with SELECT SQL_NO_CACHE.2orDEMANDCache results only for cacheable queries that begin with SELECT SQL_CACHE.This variable defaults to
OFF.If the server is started with
query_cache_typeset to 0, it does not acquire the query cache mutex at all, which means that the query cache cannot be enabled at runtime and there is reduced overhead in query execution. -
Command-Line Format --query_cache_wlock_invalidateSystem Variable Name query_cache_wlock_invalidateVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault FALSENormally, when one client acquires a
WRITElock on aMyISAMtable, other clients are not blocked from issuing statements that read from the table if the query results are present in the query cache. Setting this variable to 1 causes acquisition of aWRITElock for a table to invalidate any queries in the query cache that refer to the table. This forces other clients that attempt to access the table to wait while the lock is in effect. -
Command-Line Format --query_prealloc_size=#System Variable Name query_prealloc_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (32-bit platforms) Type integerDefault 8192Min Value 8192Max Value 4294967295Block Size 1024Permitted Values (64-bit platforms) Type integerDefault 8192Min Value 8192Max Value 18446744073709551615Block Size 1024The size of the persistent buffer used for statement parsing and execution. This buffer is not freed between statements. If you are running complex queries, a larger
query_prealloc_sizevalue might be helpful in improving performance, because it can reduce the need for the server to perform memory allocation during query execution operations. The
rand_seed1andrand_seed2variables exist as session variables only, and can be set but not read. The variables—but not their values—are shown in the output ofSHOW VARIABLES.The purpose of these variables is to support replication of the
RAND()function. For statements that invokeRAND(), the master passes two values to the slave, where they are used to seed the random number generator. The slave uses these values to set the session variablesrand_seed1andrand_seed2so thatRAND()on the slave generates the same value as on the master.See the description for
rand_seed1.-
Command-Line Format --range_alloc_block_size=#System Variable Name range_alloc_block_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (>= 5.7.9) Type integerDefault 4096Min Value 4096Max Value 4294967295Block Size 1024Permitted Values (32-bit platforms, <= 5.7.8) Type integerDefault 4096Min Value 4096Max Value 4294967295Block Size 1024Permitted Values (64-bit platforms, <= 5.7.8) Type integerDefault 4096Min Value 4096Max Value 18446744073709551615Block Size 1024Permitted Values (64-bit platforms, >= 5.7.8) Type integerDefault 4096Min Value 4096Max Value 18446744073709547520Block Size 1024The size of blocks that are allocated when doing range optimization.
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Introduced 5.7.9 Command-Line Format --range_optimizer_max_mem_size=NSystem Variable Name range_optimizer_max_mem_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (<= 5.7.11) Type integerDefault 1536000Permitted Values (>= 5.7.12) Type integerDefault 8388608The limit on memory consumption for the range optimizer. A value of 0 means “no limit.” If an execution plan considered by the optimizer uses the range access method but the optimizer estimates that the amount of memory needed for this method would exceed the limit, it abandons the plan and considers other plans. For more information, see Section 9.2.1.3.4, “Limiting Memory Use for Range Optimization”.
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Introduced 5.7.1 System Variable Name rbr_exec_modeVariable Scope Session Dynamic Variable Yes Permitted Values Type enumerationDefault STRICTValid Values IDEMPOTENTSTRICTThis variable switches the server between
IDEMPOTENTmode andSTRICTmode.IDEMPOTENTmode causes suppression of duplicate-key and no-key-found errors. This mode is useful when replaying a row-based binary log on a server that causes conflicts with existing data. mysqlbinlog uses this mode when you set the--idempotentoption by writing the following to the output:SET SESSION RBR_EXEC_MODE=IDEMPOTENT;
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Command-Line Format --read_buffer_size=#System Variable Name read_buffer_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 131072Min Value 8200Max Value 2147479552Each thread that does a sequential scan for a
MyISAMtable allocates a buffer of this size (in bytes) for each table it scans. If you do many sequential scans, you might want to increase this value, which defaults to 131072. The value of this variable should be a multiple of 4KB. If it is set to a value that is not a multiple of 4KB, its value will be rounded down to the nearest multiple of 4KB.This option is also used in the following context for all storage engines:
For caching the indexes in a temporary file (not a temporary table), when sorting rows for
ORDER BY.For bulk insert into partitions.
For caching results of nested queries.
and in one other storage engine-specific way: to determine the memory block size for
MEMORYtables.The maximum permissible setting for
read_buffer_sizeis 2GB.For more information about memory use during different operations, see Section 9.12.5.1, “How MySQL Uses Memory”.
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Command-Line Format --read_onlySystem Variable Name read_onlyVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFWhen the
read_onlysystem variable is enabled, the server permits no client updates except from users who have theSUPERprivilege. This variable is disabled by default.As of MySQL 5.7.8, the server also supports a
super_read_onlysystem variable (disabled by default), which has these effects:If
super_read_onlyis enabled, the server prohibits client updates, even from users who have theSUPERprivilege.Setting
super_read_onlytoONimplicitly forcesread_onlytoON.Setting
read_onlytoOFFimplicitly forcessuper_read_onlytoOFF.
Even with
read_onlyenabled, the server permits these operations:Updates performed by slave threads, if the server is a replication slave. In replication setups, it can be useful to enable
read_onlyon slave servers to ensure that slaves accept updates only from the master server and not from clients.Use of
ANALYZE TABLEorOPTIMIZE TABLEstatements. The purpose of read-only mode is to prevent changes to table structure or contents. Analysis and optimization do not qualify as such changes. This means, for example, that consistency checks on read-only replication slaves can be performed with mysqlcheck --all-databases --analyze.Operations on
TEMPORARYtables.Inserts into the log tables (
mysql.general_logandmysql.slow_log); see Section 6.4.1, “Selecting General Query and Slow Query Log Output Destinations”.
Changes to
read_onlyon a master server are not replicated to slave servers. The value can be set on a slave server independent of the setting on the master.The following conditions apply to attempts to enable
read_only(including implicit attempts resulting from enablingsuper_read_only):The attempt fails and an error occurs if you have any explicit locks (acquired with
LOCK TABLES) or have a pending transaction.The attempt blocks while other clients hold explicit table locks or have pending transactions, until the locks are released and the transactions end. While the attempt to enable
read_onlyis pending, requests by other clients for table locks or to begin transactions also block untilread_onlyhas been set.The attempt blocks if there are active transactions that hold metadata locks, until those transactions end.
read_onlycan be enabled while you hold a global read lock (acquired withFLUSH TABLES WITH READ LOCK) because that does not involve table locks.
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Command-Line Format --read_rnd_buffer_size=#System Variable Name read_rnd_buffer_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 262144Min Value 1Max Value 2147483647This variable is used for reads from
MyISAMtables, and, for any storage engine, for Multi-Range Read optimization.When reading rows from a
MyISAMtable in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. See Section 9.2.1.15, “ORDER BY Optimization”. Setting the variable to a large value can improveORDER BYperformance by a lot. However, this is a buffer allocated for each client, so you should not set the global variable to a large value. Instead, change the session variable only from within those clients that need to run large queries.The maximum permissible setting for
read_rnd_buffer_sizeis 2GB.For more information about memory use during different operations, see Section 9.12.5.1, “How MySQL Uses Memory”. For information about Multi-Range Read optimization, see Section 9.2.1.13, “Multi-Range Read Optimization”.
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Command-Line Format --relay_log_purgeSystem Variable Name relay_log_purgeVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault TRUEDisables or enables automatic purging of relay log files as soon as they are not needed any more. The default value is 1 (
ON). -
Command-Line Format --relay_log_space_limit=#System Variable Name relay_log_space_limitVariable Scope Global Dynamic Variable No Permitted Values (32-bit platforms) Type integerDefault 0Min Value 0Max Value 4294967295Permitted Values (64-bit platforms) Type integerDefault 0Min Value 0Max Value 18446744073709551615The maximum amount of space to use for all relay logs.
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Command-Line Format --report-host=host_nameSystem Variable Name report_hostVariable Scope Global Dynamic Variable No Permitted Values Type stringThe value of the
--report-hostoption. -
Command-Line Format --report-password=nameSystem Variable Name report_passwordVariable Scope Global Dynamic Variable No Permitted Values Type stringThe value of the
--report-passwordoption. Not the same as the password used for the MySQL replication user account. -
Command-Line Format --report-port=#System Variable Name report_portVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault [slave_port]Min Value 0Max Value 65535The value of the
--report-portoption. -
Command-Line Format --report-user=nameSystem Variable Name report_userVariable Scope Global Dynamic Variable No Permitted Values Type stringThe value of the
--report-useroption. Not the same as the name for the MySQL replication user account. -
Introduced 5.7.8 Command-Line Format --require_secure_transport[={OFF|ON}]System Variable Name require_secure_transportVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFWhether client connections to the server are required to use some form of secure transport. When this variable is enabled, the server permits only TCP/IP connections that use SSL, or connections that use a socket file (on Unix) or shared memory (on Windows). The server rejects nonsecure connection attempts, which fail with an
ER_SECURE_TRANSPORT_REQUIREDerror.This capability supplements per-account SSL requirements, which take precedence. For exmaple, if an account is defined with
REQUIRE SSL, enablingrequire_secure_transportdoes not make it possible to use the account to connect using a Unix socket file.It is possible for a server to have no secure transports available. For example, a server on Windows supports no secure transports if started without specifying any SSL certificate or key files and with the
shared_memorysystem variable disabled. Under these conditions, attempts to enablerequire_secure_transportat startup cause the server to write a message to the error log and exit. Attempts to enable the variable at runtime fail with anER_NO_SECURE_TRANSPORTS_CONFIGUREDerror. -
System Variable Name rpl_semi_sync_master_enabledVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFControls whether semisynchronous replication is enabled on the master. To enable or disable the plugin, set this variable to
ONorOFF(or 1 or 0), respectively. The default isOFF.This variable is available only if the master-side semisynchronous replication plugin is installed.
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System Variable Name rpl_semi_sync_master_timeoutVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 10000A value in milliseconds that controls how long the master waits on a commit for acknowledgment from a slave before timing out and reverting to asynchronous replication. The default value is 10000 (10 seconds).
This variable is available only if the master-side semisynchronous replication plugin is installed.
rpl_semi_sync_master_trace_levelSystem Variable Name rpl_semi_sync_master_trace_levelVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 32The semisynchronous replication debug trace level on the master. Four levels are defined:
1 = general level (for example, time function failures)
16 = detail level (more verbose information)
32 = net wait level (more information about network waits)
64 = function level (information about function entry and exit)
This variable is available only if the master-side semisynchronous replication plugin is installed.
rpl_semi_sync_master_wait_for_slave_countIntroduced 5.7.3 System Variable Name rpl_semi_sync_master_wait_for_slave_countVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 1Min Value 1Max Value 65535The number of slave acknowledgments the master must receive per transaction before proceeding. By default
rpl_semi_sync_master_wait_for_slave_countis1, meaning that semisynchronous replication proceeds after receiving a single slave acknowledgment. Performance is best for small values of this variable.For example, if
rpl_semi_sync_master_wait_for_slave_countis2, then 2 slaves must acknowledge receipt of the transaction before the timeout period configured byrpl_semi_sync_master_timeoutfor semisynchronous replication to proceed. If less slaves acknowledge receipt of the transaction during the timeout period, the master reverts to normal replication.NoteThis behavior also depends on
rpl_semi_sync_master_wait_no_slaveThis variable is available only if the master-side semisynchronous replication plugin is installed.
rpl_semi_sync_master_wait_no_slaveSystem Variable Name rpl_semi_sync_master_wait_no_slaveVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault ONControls whether the master waits for the timeout period configured by
rpl_semi_sync_master_timeoutto expire, even if the slave count drops to less than the number of slaves configured byrpl_semi_sync_master_wait_for_slave_countduring the timeout period.When the value of
rpl_semi_sync_master_wait_no_slaveisON(the default), it is permissible for the slave count to drop to less thanrpl_semi_sync_master_wait_for_slave_countduring the timeout period. As long as enough slaves acknowledge the transaction before the timeout period expires, semisynchronous replication continues.When the value of
rpl_semi_sync_master_wait_no_slaveisOFF, if the slave count drops to less than the number configured inrpl_semi_sync_master_wait_for_slave_countat any time during the timeout period configured byrpl_semi_sync_master_timeout, the master reverts to normal replication.This variable is available only if the master-side semisynchronous replication plugin is installed.
rpl_semi_sync_master_wait_pointIntroduced 5.7.2 System Variable Name rpl_semi_sync_master_wait_pointVariable Scope Global Dynamic Variable Yes Permitted Values Type enumerationDefault AFTER_SYNCValid Values AFTER_SYNCAFTER_COMMITThis variable controls the point at which a semisynchronous replication master waits for slave acknowledgment of transaction receipt before returning a status to the client that committed the transaction. These values are permitted:
AFTER_SYNC(the default): The master writes each transaction to its binary log and the slave, and syncs the binary log to disk. The master waits for slave acknowledgment of transaction receipt after the sync. Upon receiving acknowledgment, the master commits the transaction to the storage engine and returns a result to the client, which then can proceed.AFTER_COMMIT: The master writes each transaction to its binary log and the slave, syncs the binary log, and commits the transaction to the storage engine. The master waits for slave acknowledgment of transaction receipt after the commit. Upon receiving acknowledgment, the master returns a result to the client, which then can proceed.
The replication characteristics of these settings differ as follows:
With
AFTER_SYNC, all clients see the committed transaction at the same time: After it has been acknowledged by the slave and committed to the storage engine on the master. Thus, all clients see the same data on the master.In the event of master failure, all transactions committed on the master have been replicated to the slave (saved to its relay log). A crash of the master and failover to the slave is lossless because the slave is up to date.
With
AFTER_COMMIT, the client issuing the transaction gets a return status only after the server commits to the storage engine and receives slave acknowledgment. After the commit and before slave acknowledgment, other clients can see the committed transaction before the committing client.If something goes wrong such that the slave does not process the transaction, then in the event of a master crash and failover to the slave, it is possible that such clients will see a loss of data relative to what they saw on the master.
This variable is available only if the master-side semisynchronous replication plugin is installed.
rpl_semi_sync_master_wait_pointwas added in MySQL 5.7.2. For older versions, semisynchronous master behavior is equivalent to a setting ofAFTER_COMMIT.This change introduces a version compatibility constraint because it increments the semisynchronous interface version: Servers for MySQL 5.7.2 and up do not work with semisynchronous replication plugins from older versions, nor do servers from older versions work with semisynchronous replication plugins for MySQL 5.7.2 and up.
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System Variable Name rpl_semi_sync_slave_enabledVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFControls whether semisynchronous replication is enabled on the slave. To enable or disable the plugin, set this variable to
ONorOFF(or 1 or 0), respectively. The default isOFF.This variable is available only if the slave-side semisynchronous replication plugin is installed.
rpl_semi_sync_slave_trace_levelSystem Variable Name rpl_semi_sync_slave_trace_levelVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 32The semisynchronous replication debug trace level on the slave. See
rpl_semi_sync_master_trace_levelfor the permissible values.This variable is available only if the slave-side semisynchronous replication plugin is installed.
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Deprecated 5.7.5 Command-Line Format --secure-authSystem Variable Name secure_authVariable Scope Global Dynamic Variable Yes Permitted Values (<= 5.7.4) Type booleanDefault ONValid Values OFFONPermitted Values (>= 5.7.5) Type booleanDefault ONValid Values ONIf this variable is enabled, the server blocks connections by clients that attempt to use accounts that have passwords stored in the old (pre-4.1) format.
Enable this variable to prevent all use of passwords employing the old format (and hence insecure communication over the network).
As of MySQL 5.7.5, this variable is deprecated and will be removed in a future MySQL release. It is always enabled and attempting to disable it produces an error. Before MySQL 5.7.5, this variable is enabled by default but can be disabled.
Server startup fails with an error if this variable is enabled and the privilege tables are in pre-4.1 format. See Section B.5.2.4, “Client does not support authentication protocol”.
NotePasswords that use the pre-4.1 hashing method are less secure than passwords that use the native password hashing method and should be avoided. Pre-4.1 passwords are deprecated and support for them is removed in MySQL 5.7.5. For account upgrade instructions, see Section 7.5.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.
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Command-Line Format --secure-file-priv=dir_nameSystem Variable Name secure_file_privVariable Scope Global Dynamic Variable No Permitted Values (<= 5.7.5) Type stringDefault emptyValid Values emptydirnamePermitted Values (>= 5.7.6) Type stringDefault platform specificValid Values emptydirnameNULLThis variable is used to limit the effect of data import and export operations, such as those performed by the
LOAD DATAandSELECT ... INTO OUTFILEstatements and theLOAD_FILE()function. These operations are permitted only to users who have theFILEprivilege.secure_file_privmay be set as follows:If empty, the variable has no effect.
If set to the name of a directory, the server limits import and export operations to work only with files in that directory. The directory must exist; the server will not create it.
If set to
NULL, the server disables import and export operations. This value is permitted as of MySQL 5.7.6.
Before MySQL 5.7.6, this variable is empty by default. As of 5.7.6, the default value is platform specific and depends on the value of the
INSTALL_LAYOUTCMake option, as shown in the following table. To specify the defaultsecure_file_privvalue explicitly if you are building from source, use theINSTALL_SECURE_FILE_PRIVDIRCMake option.INSTALL_LAYOUTValueDefault secure_file_privValueSTANDALONE,WINempty DEB,RPM,SLES,SVR4/var/lib/mysql-filesOtherwise mysql-filesunder theCMAKE_INSTALL_PREFIXvalueAs of MySQL 5.7.8, to set the default
secure_file_privvalue for thelibmysqldembedded server, use theINSTALL_SECURE_FILE_PRIV_EMBEDDEDDIRCMake option. The default value for this option isNULL.As of MySQL 5.7.6, the server checks the value of
secure_file_privat startup and writes a warning to the error log if the value is insecure. The setting is considered insecure ifsecure_file_privhas an empty value, or the value is the data directory or a subdirectory of it, or a directory that is accessible by all users. Ifsecure_file_privis set to a nonexistent path, the server writes an error message to the error log and exits. -
Command-Line Format --server-id=#System Variable Name server_idVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 0Min Value 0Max Value 4294967295The server ID, used in replication to give each master and slave a unique identity. This variable is set by the
--server-idoption. For each server participating in replication, you should pick a positive integer in the range from 1 to 232 − 1 to act as that server's ID. -
Introduced 5.7.6 Command-Line Format --session_track_gtids=[value]System Variable Name session_track_gtidsVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type enumerationDefault OFFValid Values OFFOWN_GTIDALL_GTIDSControls a tracker for capturing GTIDs and returning them in the OK packet. Depending on the value of this option, at the end of executing a transaction, the GTIDs specified are captured by the tracker and appended to the OK packet. The possible sets of GTIDs to track are:
OFFmeans that no GTIDs are included in the OK packet. This is the same behavior as versions of MySQL prior to 5.7.6.OWN_GTIDconfigures the tracker to collect GTIDs generated by successfully committed read/write transactions.ALL_GTIDSconfigures the tracker to collect all of the GTIDs ingtid_executedat the time the current transaction commits, regardless of whether the transaction is read/write or read-only.
For information about obtaining session state-change information within client programs, see Section 25.8.7.65, “mysql_session_track_get_first()”.
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Introduced 5.7.4 Command-Line Format --session_track_schema=#System Variable Name session_track_schemaVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault ONControls whether the server tracks changes to the default schema (database) name within the current session and makes this information available to the client when changes occur.
If notification is enabled, any setting of the default schema is reported, even if the new schema name is the same as the old.
For information about obtaining session state-change information within client programs, see Section 25.8.7.65, “mysql_session_track_get_first()”.
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Introduced 5.7.4 Command-Line Format --session_track_state_change=#System Variable Name session_track_state_changeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault OFFControls whether the server tracks changes to the state of the current session and notifies the client when state changes occur. Session state consists of these values:
The default schema (database)
Session-specific values for system variables
User-defined variables
Temporary tables
Prepared statements
If the session-state tracker is enabled, any assignments to session state values are reported, even if the new values are the same as the old.
The
session_track_state_changevariable controls only notification of when changes occur, not what the changes are. To receive notification for changes to the default schema name and session system variable values, use thesession_track_schemaandsession_track_system_variablessystem variables.For information about obtaining session state-change information within client programs, see Section 25.8.7.65, “mysql_session_track_get_first()”.
session_track_system_variablesIntroduced 5.7.4 Command-Line Format --session_track_system_variables=#System Variable Name session_track_system_variablesVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringDefault time_zone, autocommit, character_set_client, character_set_results, character_set_connectionControls whether the server tracks changes to the session system variables and makes this information available to the client when changes occur. The variable value is a comma-separated list of variables for which to track changes. By default, notification is enabled for
time_zone,autocommit,character_set_client,character_set_results, andcharacter_set_connection. (The latter three variables are those affected bySET NAMES.)The special value
*causes the server to track changes to all session variables. If given, this value must be specified by itself without specific system variable names.Notification occurs for all assignments to tracked session system variables, even if the new values are the same as the old.
For information about obtaining session state-change information within client programs, see Section 25.8.7.65, “mysql_session_track_get_first()”.
sha256_password_auto_generate_rsa_keysIntroduced 5.7.5 Command-Line Format --sha256_password_auto_generate_rsa_keys[={OFF|ON}]System Variable Name sha256_password_auto_generate_rsa_keysVariable Scope Global Dynamic Variable No Permitted Values Type booleanDefault ONThis variable is available if the server was compiled using OpenSSL (see Section 7.4.1, “OpenSSL Versus yaSSL”). It controls whether the server autogenerates RSA private/public key-pair files in the data directory, if they do not already exist.
At startup, the server automatically generates RSA private/public key-pair files in the data directory if the
sha256_password_auto_generate_rsa_keyssystem variable is enabled, no RSA options are specified, and the RSA files are missing from the data directory. These files enable secure password exchange using RSA over unencrypted connections for accounts authenticated by thesha256_passwordplugin; see Section 7.5.1.4, “The SHA-256 Authentication Plugin”.For more information about RSA file autogeneration, including file names and characteristics, see Section 7.4.6.1, “Creating SSL and RSA Certificates and Keys using MySQL”
The
auto_generate_certssystem variable is related but controls autogeneration of SSL certificate and key files needed for secure connections using SSL.sha256_password_private_key_pathSystem Variable Name sha256_password_private_key_pathVariable Scope Global Dynamic Variable No Permitted Values Type file nameDefault private_key.pemThis variable is available if MySQL was compiled using OpenSSL (see Section 7.4.1, “OpenSSL Versus yaSSL”). Its value is the path name of the RSA private key file for the
sha256_passwordauthentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format. Because this file stores a private key, its access mode should be restricted so that only the MySQL server can read it.For information about
sha256_password, including instructions for creating the RSA key files, see Section 7.5.1.4, “The SHA-256 Authentication Plugin”.-
Introduced 5.7.7 Command-Line Format --sha256_password_proxy_users=[={OFF|ON}]System Variable Name sha256_password_proxy_usersVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFThis variable controls whether the
sha256_passwordbuilt-in authentication plugin supports proxy users. It has no effect unless thecheck_proxy_userssystem variable is enabled. For information about user proxying, see Section 7.3.9, “Proxy Users”.This variable was added in MySQL 5.7.7. Before 5.7.7,
sha256_passworddoes not support proxy users. sha256_password_public_key_pathSystem Variable Name sha256_password_public_key_pathVariable Scope Global Dynamic Variable No Permitted Values Type file nameDefault public_key.pemThis variable is available if MySQL was compiled using OpenSSL (see Section 7.4.1, “OpenSSL Versus yaSSL”). Its value is the path name of the RSA public key file for the
sha256_passwordauthentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format. Because this file stores a public key, copies can be freely distributed to client users. (Clients that explicitly specify a public key when connecting to the server using RSA password encryption must use the same public key as that used by the server.)For information about
sha256_password, including instructions for creating the RSA key files and how clients specify the RSA public key, see Section 7.5.1.4, “The SHA-256 Authentication Plugin”.-
Command-Line Format --shared_memory[={0,1}]System Variable Name shared_memoryVariable Scope Global Dynamic Variable No Platform Specific Windows Permitted Values Type booleanDefault FALSE(Windows only.) Whether the server permits shared-memory connections.
-
Command-Line Format --shared_memory_base_name=nameSystem Variable Name shared_memory_base_nameVariable Scope Global Dynamic Variable No Platform Specific Windows Permitted Values Type stringDefault MYSQL(Windows only.) The name of shared memory to use for shared-memory connections. This is useful when running multiple MySQL instances on a single physical machine. The default name is
MYSQL. The name is case sensitive. -
Introduced 5.7.6 Deprecated 5.7.6 Command-Line Format --show_compatibility_56[={OFF|ON}]System Variable Name show_compatibility_56Variable Scope Global Dynamic Variable Yes Permitted Values (<= 5.7.7) Type booleanDefault ONPermitted Values (>= 5.7.8) Type booleanDefault OFFThe
INFORMATION_SCHEMAhas tables that contain system and status variable information (see Section 22.10, “The INFORMATION_SCHEMA GLOBAL_VARIABLES and SESSION_VARIABLES Tables”, and Section 22.9, “The INFORMATION_SCHEMA GLOBAL_STATUS and SESSION_STATUS Tables”). As of MySQL 5.7.6, the Performance Schema also contains system and status variable tables (see Section 23.9.13, “Performance Schema System Variable Tables”, and Section 23.9.14, “Performance Schema Status Variable Tables”). The Performance Schema tables are intended to replace theINFORMATION_SCHEMAtables, which are deprecated as of MySQL 5.7.6 and will be removed in a future MySQL release.For advice on migrating away from the
INFORMATION_SCHEMAtables to the Performance Schema tables, see Section 23.17, “Migrating to Performance Schema System and Status Variable Tables”. To assist in the migration, you can use theshow_compatibility_56system variable, which affects whether MySQL 5.6 compatibility is enabled with respect to how system and status variable information is provided by theINFORMATION_SCHEMAand Performance Schema tables, and also by theSHOW VARIABLESandSHOW STATUSstatements.Noteshow_compatibility_56is deprecated because its only purpose is to permit control over deprecated system and status variable information sources that will be removed in a future MySQL release. When those sources are removed,show_compatibility_56will have no purpose and will be removed as well.The following discussion describes the effects of
show_compatibility_56:For better understanding, it is strongly recommended that you also read these sections:
Overview of show_compatibility_56 Effects
The
show_compatibility_56system variable affects these aspects of server operation regarding system and status variables:Information available from the
SHOW VARIABLESandSHOW STATUSstatementsInformation available from the
INFORMATION_SCHEMAtables that provide system and status variable informationInformation available from the Performance Schema tables that provide system and status variable information
The effect of the
FLUSH STATUSstatement on status variables
This list summarizes the effects of
show_compatibility_56, with additional details given later:When
show_compatibility_56isON, compatibility with MySQL 5.6 is enabled. Older variable information sources (SHOWstatements,INFORMATION_SCHEMAtables) produce the same output as in MySQL 5.6.When
show_compatibility_56isOFF, compatibility with MySQL 5.6 is disabled. Selecting from theINFORMATION_SCHEMAtables produces an error because the Performance Schema tables are intended to replace them. TheINFORMATION_SCHEMAtables are deprecated as of MySQL 5.7.6 and will be removed in a future MySQL release.To obtain system and status variable information When
show_compatibility_56=OFF, use the Performance Schema tables or theSHOWstatements.NoteWhen
show_compatibility_56=OFF, theSHOW VARIABLESandSHOW STATUSstatements display rows from the Performance Schemaglobal_variables,session_variables,global_status, andsession_statustables.As of MySQL 5.7.9, those tables are world readable and accessible without the
SELECTprivilege, which means thatSELECTis not needed to use theSHOWstatements, either. Before MySQL 5.7.9, theSELECTprivilege is required to access those Performance Schema tables, either directly, or indirectly through theSHOWstatements.Several
Slave_status variables are available fromxxxSHOW STATUSwhenshow_compatibility_56isON. Whenshow_compatibility_56isOFF, some of those variables are not exposed toSHOW STATUS. The information they provide is available in replication-related Performance Schema tables, as described later.show_compatibility_56has no effect on system variable access using@@notation:@@GLOBAL.,var_name@@SESSION.,var_name@@.var_nameshow_compatibility_56has no effect for the embedded server, which produces 5.6-compatible output in all cases.
The following descriptions detail the effect of setting
show_compatibility_56toONorOFFin the contexts in which this variable applies.Effect of show_compatibility_56 on SHOW Statements
SHOW GLOBAL VARIABLESstatement:ON: MySQL 5.6 output.OFF: Output displays rows from the Performance Schemaglobal_variablestable.
SHOW [SESSION | LOCAL] VARIABLESstatement:ON: MySQL 5.6 output.OFF: Output displays rows from the Performance Schemasession_variablestable. (In MySQL 5.7.6 and 5.7.7,OFFoutput does not fully reflect all system variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)
SHOW GLOBAL STATUSstatement:ON: MySQL 5.6 output.OFF: Output displays rows from the Performance Schemaglobal_statustable, plus theCom_statement execution counters.xxxOFFoutput includes no rows for session variables that have no global counterpart, unlikeONoutput.
SHOW [SESSION | LOCAL] STATUSstatement:ON: MySQL 5.6 output.OFF: Output displays rows from the Performance Schemasession_statustable, plus theCom_statement execution counters. (In MySQL 5.7.6 and 5.7.7,xxxOFFoutput does not fully reflect all status variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)
In MySQL 5.7.6 and 5.7.7, for each of the
SHOWstatements just described, use of aWHEREclause produces a warning whenshow_compatibility_56=ONand an error whenshow_compatibility_56=OFF. (This applies toWHEREclauses that are not optimized away. For example,WHERE 1is trivially true, is optimized away, and thus produces no warning or error.) This behavior does not occur as of MySQL 5.7.8;WHEREis supported as before 5.7.6.Effect of show_compatibility_56 on INFORMATION_SCHEMA Tables
INFORMATION_SCHEMAtables (GLOBAL_VARIABLES,SESSION_VARIABLES,GLOBAL_STATUS, andSESSION_STATUS):ON: MySQL 5.6 output, with a deprecation warning.OFF: Selecting from these tables produces an error. (Before 5.7.9, selecting from these tables produces no output, with a deprecation warning.)
Effect of show_compatibility_56 on Performance Schema Tables
Performance Schema system variable tables:
OFF:global_variables: Global system variables only.session_variables: System variables in effect for the current session: A row for each session variable, and a row for each global variable that has no session counterpart. (In MySQL 5.7.6 and 5.7.7, the table does not fully reflect all system variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)variables_by_thread: Session system variables only, for each active session.
ON: Same output as forOFF. (Before 5.7.8, these tables produce no output.)
Performance Schema status variable tables:
OFF:global_status: Global status variables only.session_status: Status variables in effect the current session: A row for each session variable, and a row for each global variable that has no session counterpart. (In MySQL 5.7.6 and 5.7.7, the table does not fully reflect all status variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)status_by_accountSession status variables only, aggregated per account.status_by_host: Session status variables only, aggregated per host name.status_by_thread: Session status variables only, for each active session.status_by_user: Session status variables only, aggregated per user name.
ON: Same output as forOFF. (Before 5.7.9, these tables produce no output.)
Effect of show_compatibility_56 on Slave Status Variables
Slave status variables:
ON: SeveralSlave_status variables are available fromxxxSHOW STATUS.OFF: Some of those slave variables are not exposed toSHOW STATUSor the Performance Schema status variable tables. The information they provide is available in replication-related Performance Schema tables. The following table shows whichSlave_status variables become unavailable inxxxSHOW STATUSand their locations in Performance Schema replication tables.Status Variable Performance Schema Location Slave_heartbeat_periodreplication_connection_configurationtable,HEARTBEAT_INTERVALcolumnSlave_last_heartbeatreplication_connection_statustable,LAST_HEARTBEAT_TIMESTAMPcolumnSlave_received_heartbeatsreplication_connection_statustable,COUNT_RECEIVED_HEARTBEATScolumnSlave_retried_transactionsreplication_applier_statustable,COUNT_TRANSACTIONS_RETRIEScolumnSlave_runningreplication_connection_statusandreplication_applier_statustables,SERVICE_STATEcolumn
Effect of show_compatibility_56 on FLUSH STATUS
FLUSH STATUSstatement:ON: This statement produces MySQL 5.6 behavior. It adds the current thread's session status variable values to the global values and resets the session values to zero. Some global variables may be reset to zero as well. It also resets the counters for key caches (default and named) to zero and setsMax_used_connectionsto the current number of open connections.OFF: This statement adds the session status from all active sessions to the global status variables, resets the status of all active sessions, and resets account, host, and user status values aggregated from disconnected sessions.
-
Introduced 5.7.6 Deprecated 5.7.6 Command-Line Format --show_old_temporals={OFF|ON}System Variable Name show_old_temporalsVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault OFFWhether
SHOW CREATE TABLEoutput includes comments to flag temporal columns found to be in pre-5.6.4 format (TIME,DATETIME, andTIMESTAMPcolumns without support for fractional seconds precision). This variable is disabled by default. If enabled,SHOW CREATE TABLEoutput looks like this:CREATE TABLE `mytbl` ( `ts` timestamp /* 5.5 binary format */ NOT NULL DEFAULT CURRENT_TIMESTAMP, `dt` datetime /* 5.5 binary format */ DEFAULT NULL, `t` time /* 5.5 binary format */ DEFAULT NULL ) DEFAULT CHARSET=latin1
Output for the
COLUMN_TYPEcolumn of theINFORMATION_SCHEMA.COLUMNStable is affected similarly.This variable is deprecated and will be removed in a future MySQL release.
-
Command-Line Format --skip-external-lockingSystem Variable Name skip_external_lockingVariable Scope Global Dynamic Variable No Permitted Values Type booleanDefault ONThis is
OFFif mysqld uses external locking (system locking),ONif external locking is disabled. This affects onlyMyISAMtable access.This variable is set by the
--external-lockingor--skip-external-lockingoption. External locking is disabled by default.External locking affects only
MyISAMtable access. For more information, including conditions under which it can and cannot be used, see Section 9.11.5, “External Locking”. -
Command-Line Format --skip-name-resolveSystem Variable Name skip_name_resolveVariable Scope Global Dynamic Variable No Permitted Values Type booleanDefault OFFThis variable is set from the value of the
--skip-name-resolveoption. If it isOFF, mysqld resolves host names when checking client connections. If it isON, mysqld uses only IP numbers; in this case, allHostcolumn values in the grant tables must be IP addresses orlocalhost. See Section 9.12.6.2, “DNS Lookup Optimization and the Host Cache”. -
Command-Line Format --skip-networkingSystem Variable Name skip_networkingVariable Scope Global Dynamic Variable No This is
ONif the server permits only local (non-TCP/IP) connections. On Unix, local connections use a Unix socket file. On Windows, local connections use a named pipe or shared memory. This variable can be set toONwith the--skip-networkingoption. -
Command-Line Format --skip-show-databaseSystem Variable Name skip_show_databaseVariable Scope Global Dynamic Variable No This prevents people from using the
SHOW DATABASESstatement if they do not have theSHOW DATABASESprivilege. This can improve security if you have concerns about users being able to see databases belonging to other users. Its effect depends on theSHOW DATABASESprivilege: If the variable value isON, theSHOW DATABASESstatement is permitted only to users who have theSHOW DATABASESprivilege, and the statement displays all database names. If the value isOFF,SHOW DATABASESis permitted to all users, but displays the names of only those databases for which the user has theSHOW DATABASESor other privilege. (Note that any global privilege is considered a privilege for the database.) -
Command-Line Format --slow_launch_time=#System Variable Name slow_launch_timeVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 2If creating a thread takes longer than this many seconds, the server increments the
Slow_launch_threadsstatus variable. -
Command-Line Format --slow-query-logSystem Variable Name slow_query_logVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFWhether the slow query log is enabled. The value can be 0 (or
OFF) to disable the log or 1 (orON) to enable the log. The default value depends on whether the--slow_query_logoption is given. The destination for log output is controlled by thelog_outputsystem variable; if that value isNONE, no log entries are written even if the log is enabled.“Slow” is determined by the value of the
long_query_timevariable. See Section 6.4.5, “The Slow Query Log”. -
Command-Line Format --slow-query-log-file=file_nameSystem Variable Name slow_query_log_fileVariable Scope Global Dynamic Variable Yes Permitted Values Type file nameDefault host_name-slow.logThe name of the slow query log file. The default value is
host_name-slow.log--slow_query_log_fileoption. -
Command-Line Format --socket={file_name|pipe_name}System Variable Name socketVariable Scope Global Dynamic Variable No Permitted Values Type stringDefault /tmp/mysql.sockOn Unix platforms, this variable is the name of the socket file that is used for local client connections. The default is
/tmp/mysql.sock. (For some distribution formats, the directory might be different, such as/var/lib/mysqlfor RPMs.)On Windows, this variable is the name of the named pipe that is used for local client connections. The default value is
MySQL(not case sensitive). -
Command-Line Format --sort_buffer_size=#System Variable Name sort_buffer_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (Windows) Type integerDefault 262144Min Value 32768Max Value 4294967295Permitted Values (Other, 32-bit platforms) Type integerDefault 262144Min Value 32768Max Value 4294967295Permitted Values (Other, 64-bit platforms) Type integerDefault 262144Min Value 32768Max Value 18446744073709551615Each session that must perform a sort allocates a buffer of this size.
sort_buffer_sizeis not specific to any storage engine and applies in a general manner for optimization. At minimum thesort_buffer_sizevalue must be large enough to accommodate fifteen tuples in the sort buffer. Also, increasing the value ofmax_sort_lengthmay require increasing the value ofsort_buffer_size. For more information, see Section 9.2.1.15, “ORDER BY Optimization”If you see many
Sort_merge_passesper second inSHOW GLOBAL STATUSoutput, you can consider increasing thesort_buffer_sizevalue to speed upORDER BYorGROUP BYoperations that cannot be improved with query optimization or improved indexing.The optimizer tries to work out how much space is needed but can allocate more, up to the limit. Setting it larger than required globally will slow down most queries that sort. It is best to increase it as a session setting, and only for the sessions that need a larger size. On Linux, there are thresholds of 256KB and 2MB where larger values may significantly slow down memory allocation, so you should consider staying below one of those values. Experiment to find the best value for your workload. See Section B.5.3.5, “Where MySQL Stores Temporary Files”.
The maximum permissible setting for
sort_buffer_sizeis 4GB−1. Larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB−1 with a warning). -
System Variable Name sql_auto_is_nullVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault 0If this variable is set to 1, then after a statement that successfully inserts an automatically generated
AUTO_INCREMENTvalue, you can find that value by issuing a statement of the following form:SELECT * FROM
tbl_nameWHEREauto_colIS NULLIf the statement returns a row, the value returned is the same as if you invoked the
LAST_INSERT_ID()function. For details, including the return value after a multiple-row insert, see Section 13.14, “Information Functions”. If noAUTO_INCREMENTvalue was successfully inserted, theSELECTstatement returns no row.The behavior of retrieving an
AUTO_INCREMENTvalue by using anIS NULLcomparison is used by some ODBC programs, such as Access. See Obtaining Auto-Increment Values. This behavior can be disabled by settingsql_auto_is_nullto 0.The default value of
sql_auto_is_nullis 0. -
System Variable Name sql_big_selectsVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault 1If set to 0, MySQL aborts
SELECTstatements that are likely to take a very long time to execute (that is, statements for which the optimizer estimates that the number of examined rows exceeds the value ofmax_join_size). This is useful when an inadvisableWHEREstatement has been issued. The default value for a new connection is 1, which permits allSELECTstatements.If you set the
max_join_sizesystem variable to a value other thanDEFAULT,sql_big_selectsis set to 0. -
System Variable Name sql_buffer_resultVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault 0If set to 1,
sql_buffer_resultforces results fromSELECTstatements to be put into temporary tables. This helps MySQL free the table locks early and can be beneficial in cases where it takes a long time to send results to the client. The default value is 0. -
System Variable Name sql_log_binVariable Scope Session Dynamic Variable Yes Permitted Values Type booleanThis variable controls whether logging to the binary log is done. The default value is 1 (do logging). To change logging for the current session, change the session value of this variable. The session user must have the
SUPERprivilege to set this variable.Setting this variable to 0 prevents GTIDs from being assigned to transactions in the binary log. If you are using GTIDs for replication, this means that, even when binary logging is later enabled once again, the GTIDs written into the log from this point do not account for any transactions that occurred in the meantime—in effect, those transactions are lost.
In MySQL 5.7, it is not possible to set
@@session.sql_log_binwithin a transaction or subquery. (Bug #53437) -
System Variable Name sql_log_offVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault 0This variable controls whether logging to the general query log is done. The default value is 0 (do logging). To change logging for the current session, change the session value of this variable. The session user must have the
SUPERprivilege to set this option. The default value is 0. -
Command-Line Format --sql-mode=nameSystem Variable Name sql_modeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (<= 5.7.4) Type setDefault NO_ENGINE_SUBSTITUTIONValid Values ALLOW_INVALID_DATESANSI_QUOTESERROR_FOR_DIVISION_BY_ZEROHIGH_NOT_PRECEDENCEIGNORE_SPACENO_AUTO_CREATE_USERNO_AUTO_VALUE_ON_ZERONO_BACKSLASH_ESCAPESNO_DIR_IN_CREATENO_ENGINE_SUBSTITUTIONNO_FIELD_OPTIONSNO_KEY_OPTIONSNO_TABLE_OPTIONSNO_UNSIGNED_SUBTRACTIONNO_ZERO_DATENO_ZERO_IN_DATEONLY_FULL_GROUP_BYPAD_CHAR_TO_FULL_LENGTHPIPES_AS_CONCATREAL_AS_FLOATSTRICT_ALL_TABLESSTRICT_TRANS_TABLESPermitted Values (>= 5.7.5, <= 5.7.6) Type setDefault ONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ENGINE_SUBSTITUTIONValid Values ALLOW_INVALID_DATESANSI_QUOTESERROR_FOR_DIVISION_BY_ZEROHIGH_NOT_PRECEDENCEIGNORE_SPACENO_AUTO_CREATE_USERNO_AUTO_VALUE_ON_ZERONO_BACKSLASH_ESCAPESNO_DIR_IN_CREATENO_ENGINE_SUBSTITUTIONNO_FIELD_OPTIONSNO_KEY_OPTIONSNO_TABLE_OPTIONSNO_UNSIGNED_SUBTRACTIONNO_ZERO_DATENO_ZERO_IN_DATEONLY_FULL_GROUP_BYPAD_CHAR_TO_FULL_LENGTHPIPES_AS_CONCATREAL_AS_FLOATSTRICT_ALL_TABLESSTRICT_TRANS_TABLESPermitted Values (5.7.7) Type setDefault ONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_AUTO_CREATE_USER NO_ENGINE_SUBSTITUTIONValid Values ALLOW_INVALID_DATESANSI_QUOTESERROR_FOR_DIVISION_BY_ZEROHIGH_NOT_PRECEDENCEIGNORE_SPACENO_AUTO_CREATE_USERNO_AUTO_VALUE_ON_ZERONO_BACKSLASH_ESCAPESNO_DIR_IN_CREATENO_ENGINE_SUBSTITUTIONNO_FIELD_OPTIONSNO_KEY_OPTIONSNO_TABLE_OPTIONSNO_UNSIGNED_SUBTRACTIONNO_ZERO_DATENO_ZERO_IN_DATEONLY_FULL_GROUP_BYPAD_CHAR_TO_FULL_LENGTHPIPES_AS_CONCATREAL_AS_FLOATSTRICT_ALL_TABLESSTRICT_TRANS_TABLESPermitted Values (>= 5.7.8) Type setDefault ONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ZERO_IN_DATE NO_ZERO_DATE ERROR_FOR_DIVISION_BY_ZERO NO_AUTO_CREATE_USER NO_ENGINE_SUBSTITUTIONValid Values ALLOW_INVALID_DATESANSI_QUOTESERROR_FOR_DIVISION_BY_ZEROHIGH_NOT_PRECEDENCEIGNORE_SPACENO_AUTO_CREATE_USERNO_AUTO_VALUE_ON_ZERONO_BACKSLASH_ESCAPESNO_DIR_IN_CREATENO_ENGINE_SUBSTITUTIONNO_FIELD_OPTIONSNO_KEY_OPTIONSNO_TABLE_OPTIONSNO_UNSIGNED_SUBTRACTIONNO_ZERO_DATENO_ZERO_IN_DATEONLY_FULL_GROUP_BYPAD_CHAR_TO_FULL_LENGTHPIPES_AS_CONCATREAL_AS_FLOATSTRICT_ALL_TABLESSTRICT_TRANS_TABLESThe current server SQL mode, which can be set dynamically. For details, see Section 6.1.7, “Server SQL Modes”.
NoteMySQL installation programs may configure the SQL mode during the installation process. For example, mysql_install_db creates a default option file named
my.cnfin the base installation directory. This file contains a line that sets the SQL mode; see Section 5.4.2, “mysql_install_db — Initialize MySQL Data Directory”.If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.
If set to 1 (the default), warnings of
Notelevel incrementwarning_countand the server records them. If set to 0,Notewarnings do not incrementwarning_countand the server does not record them. mysqldump includes output to set this variable to 0 so that reloading the dump file does not produce warnings for events that do not affect the integrity of the reload operation.If set to 1 (the default), the server quotes identifiers for
SHOW CREATE TABLEandSHOW CREATE DATABASEstatements. If set to 0, quoting is disabled. This option is enabled by default so that replication works for identifiers that require quoting. See Section 14.7.5.10, “SHOW CREATE TABLE Syntax”, and Section 14.7.5.6, “SHOW CREATE DATABASE Syntax”.If set to 1, MySQL aborts
UPDATEorDELETEstatements that do not use a key in theWHEREclause or aLIMITclause. (Specifically,UPDATEstatements must have aWHEREclause that uses a key or aLIMITclause, or both.DELETEstatements must have both.) This makes it possible to catchUPDATEorDELETEstatements where keys are not used properly and that would probably change or delete a large number of rows. The default value is 0.-
System Variable Name sql_select_limitVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerThe maximum number of rows to return from
SELECTstatements. The default value for a new connection is the maximum number of rows that the server permits per table. Typical default values are (232)−1 or (264)−1. If you have changed the limit, the default value can be restored by assigning a value ofDEFAULT.If a
SELECThas aLIMITclause, theLIMITtakes precedence over the value ofsql_select_limit. This variable controls whether single-row
INSERTstatements produce an information string if warnings occur. The default is 0. Set the value to 1 to produce an information string.-
Command-Line Format --ssl-ca=file_nameSystem Variable Name ssl_caVariable Scope Global Dynamic Variable No Permitted Values Type file nameThe path to a file with a list of trusted SSL CAs.
-
Command-Line Format --ssl-capath=dir_nameSystem Variable Name ssl_capathVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe path to a directory that contains trusted SSL CA certificates in PEM format.
-
Command-Line Format --ssl-cert=file_nameSystem Variable Name ssl_certVariable Scope Global Dynamic Variable No Permitted Values Type file nameThe name of the SSL certificate file to use for establishing a secure connection.
-
Command-Line Format --ssl-cipher=nameSystem Variable Name ssl_cipherVariable Scope Global Dynamic Variable No Permitted Values Type stringA list of permissible ciphers to use for SSL encryption.
-
Command-Line Format --ssl-crl=file_nameSystem Variable Name ssl_crlVariable Scope Global Dynamic Variable No Permitted Values Type file nameThe path to a file containing certificate revocation lists in PEM format. Revocation lists work for MySQL distributions compiled using OpenSSL (but not yaSSL). See Section 7.4.1, “OpenSSL Versus yaSSL”.
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Command-Line Format --ssl-crlpath=dir_nameSystem Variable Name ssl_crlpathVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe path to a directory that contains files containing certificate revocation lists in PEM format. Revocation lists work for MySQL distributions compiled using OpenSSL (but not yaSSL). See Section 7.4.1, “OpenSSL Versus yaSSL”.
-
Command-Line Format --ssl-key=file_nameSystem Variable Name ssl_keyVariable Scope Global Dynamic Variable No Permitted Values Type file nameThe name of the SSL key file to use for establishing a secure connection.
-
Removed 5.7.5 System Variable Name storage_engineVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type enumerationDefault InnoDBThis variable is deprecated and was removed in MySQL 5.7.5. Use
default_storage_engineinstead. -
Command-Line Format --stored-program-cache=#System Variable Name stored_program_cacheVariable Scope Global Dynamic Variable Yes Permitted Values (<= 5.7.5) Type integerDefault 256Min Value 256Max Value 524288Permitted Values (>= 5.7.6) Type integerDefault 256Min Value 16Max Value 524288Sets a soft upper limit for the number of cached stored routines per connection. The value of this variable is specified in terms of the number of stored routines held in each of the two caches maintained by the MySQL Server for, respectively, stored procedures and stored functions.
Whenever a stored routine is executed this cache size is checked before the first or top-level statement in the routine is parsed; if the number of routines of the same type (stored procedures or stored functions according to which is being executed) exceeds the limit specified by this variable, the corresponding cache is flushed and memory previously allocated for cached objects is freed. This allows the cache to be flushed safely, even when there are dependencies between stored routines.
-
Introduced 5.7.8 Command-Line Format --super_read_only[={OFF|ON}]System Variable Name super_read_onlyVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFIf the
read_onlysystem variable is enabled, the server permits client updates only from users who have theSUPERprivilege. If thesuper_read_onlysystem variable is also enabled, the server prohibits client updates even from users who haveSUPER. See the description of theread_onlysystem variable for a description of read-only mode and information about howread_onlyandsuper_read_onlyinteract.Changes to
super_read_onlyon a master server are not replicated to slave servers. The value can be set on a slave server independent of the setting on the master. -
Deprecated 5.7.6 Command-Line Format --sync-frmSystem Variable Name sync_frmVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault TRUEIf this variable is set to 1, when any nontemporary table is created its
.frmfile is synchronized to disk (usingfdatasync()). This is slower but safer in case of a crash. The default is 1.This variable is deprecated in MySQL 5.7.6 and will be removed in a future version of MySQL (when
.frmfiles become obsolete). -
System Variable Name system_time_zoneVariable Scope Global Dynamic Variable No Permitted Values Type stringThe server system time zone. When the server begins executing, it inherits a time zone setting from the machine defaults, possibly modified by the environment of the account used for running the server or the startup script. The value is used to set
system_time_zone. Typically the time zone is specified by theTZenvironment variable. It also can be specified using the--timezoneoption of the mysqld_safe script.The
system_time_zonevariable differs fromtime_zone. Although they might have the same value, the latter variable is used to initialize the time zone for each client that connects. See Section 11.6, “MySQL Server Time Zone Support”. -
System Variable Name table_definition_cacheVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault -1 (autosized)Min Value 400Max Value 524288The number of table definitions (from
.frmfiles) that can be stored in the definition cache. If you use a large number of tables, you can create a large table definition cache to speed up opening of tables. The table definition cache takes less space and does not use file descriptors, unlike the normal table cache. The minimum value is 400. The default value is based on the following formula, capped to a limit of 2000:400 + (table_open_cache / 2)
For
InnoDB,table_definition_cacheacts as a soft limit for the number of open table instances in theInnoDBdata dictionary cache. If the number of open table instances exceeds thetable_definition_cachesetting, the LRU mechanism begins to mark table instances for eviction and eventually removes them from the data dictionary cache. The limit helps address situations in which significant amounts of memory would be used to cache rarely used table instances until the next server restart. The number of table instances with cached metadata could be higher than the limit defined bytable_definition_cache, becauseInnoDBsystem table instances and parent and child table instances with foreign key relationships are not placed on the LRU list and are not subject to eviction from memory.Additionally,
table_definition_cachedefines a soft limit for the number ofInnoDBfile-per-table tablespaces that can be open at one time, which is also controlled byinnodb_open_files. If bothtable_definition_cacheandinnodb_open_filesare set, the highest setting is used. If neither variable is set,table_definition_cache, which has a higher default value, is used. If the number of open tablespace file handles exceeds the limit defined bytable_definition_cacheorinnodb_open_files, the LRU mechanism searches the tablespace file LRU list for files that are fully flushed and are not currently being extended. This process is performed each time a new tablespace is opened. If there are no “inactive” tablespaces, no tablespace files are closed. -
System Variable Name table_open_cacheVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 2000Min Value 1Max Value 524288The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. You can check whether you need to increase the table cache by checking the
Opened_tablesstatus variable. See Section 6.1.6, “Server Status Variables”. If the value ofOpened_tablesis large and you do not useFLUSH TABLESoften (which just forces all tables to be closed and reopened), then you should increase the value of thetable_open_cachevariable. For more information about the table cache, see Section 9.4.3.1, “How MySQL Opens and Closes Tables”. -
System Variable Name table_open_cache_instancesVariable Scope Global Dynamic Variable No Permitted Values (<= 5.7.7) Type integerDefault 1Min Value 1Max Value 64Permitted Values (>= 5.7.8) Type integerDefault 16Min Value 1Max Value 64The number of open tables cache instances. To improve scalability by reducing contention among sessions, the open tables cache can be partitioned into several smaller cache instances of size
table_open_cache/table_open_cache_instances. A session needs to lock only one instance to access it for DML statements. This segments cache access among instances, permitting higher performance for operations that use the cache when there are many sessions accessing tables. (DDL statements still require a lock on the entire cache, but such statements are much less frequent than DML statements.)A value of 8 or 16 is recommended on systems that routinely use 16 or more cores.
-
Command-Line Format --thread_cache_size=#System Variable Name thread_cache_sizeVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault -1 (autosized)Min Value 0Max Value 16384How many threads the server should cache for reuse. When a client disconnects, the client's threads are put in the cache if there are fewer than
thread_cache_sizethreads there. Requests for threads are satisfied by reusing threads taken from the cache if possible, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. Normally, this does not provide a notable performance improvement if you have a good thread implementation. However, if your server sees hundreds of connections per second you should normally setthread_cache_sizehigh enough so that most new connections use cached threads. By examining the difference between theConnectionsandThreads_createdstatus variables, you can see how efficient the thread cache is. For details, see Section 6.1.6, “Server Status Variables”.The default value is based on the following formula, capped to a limit of 100:
8 + (max_connections / 100)
This variable has no effect for the embedded server (
libmysqld) and as of MySQL 5.7.2 is no longer visible within the embedded server. -
Deprecated 5.6.1 Removed 5.7.2 Command-Line Format --thread_concurrency=#System Variable Name thread_concurrencyVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 10Min Value 1Max Value 512This variable is specific to Solaris 8 and earlier systems, for which mysqld invokes the
thr_setconcurrency()function with the variable value. This function enables applications to give the threads system a hint about the desired number of threads that should be run at the same time. Current Solaris versions document this as having no effect.This variable was removed in MySQL 5.7.2.
-
Command-Line Format --thread_handling=nameSystem Variable Name thread_handlingVariable Scope Global Dynamic Variable No Permitted Values (<= 5.7.8) Type enumerationDefault one-thread-per-connectionValid Values no-threadsone-thread-per-connectionPermitted Values (>= 5.7.9) Type enumerationDefault one-thread-per-connectionValid Values no-threadsone-thread-per-connectiondynamically-loadedThe thread-handling model used by the server for connection threads. The permissible values are
no-threads(the server uses a single thread to handle one connection) andone-thread-per-connection(the server uses one thread to handle each client connection).no-threadsis useful for debugging under Linux; see Section 26.5, “Debugging and Porting MySQL”.This variable has no effect for the embedded server (
libmysqld) and as of MySQL 5.7.2 is no longer visible within the embedded server. -
Introduced 5.7.9 Command-Line Format --thread_pool_algorithm=#System Variable Name thread_pool_algorithmVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 0Min Value 0Max Value 1This variable controls which algorithm the thread pool plugin uses:
A value of 0 (the default) uses a conservative low-concurrency algorithm which is most well tested and is known to produce very good results.
A value of 1 increases the concurrency and uses a more aggressive algorithm which at times has been known to perform 5–10% better on optimal thread counts, but has degrading performance as the number of connections increases. Its use should be considered as experimental and not supported.
This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”
thread_pool_high_priority_connectionIntroduced 5.7.9 Command-Line Format --thread_pool_high_priority_connection=#System Variable Name thread_pool_high_priority_connectionVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 0Min Value 0Max Value 1This variable affects queuing of new statements prior to execution. If the value is 0 (false, the default), statement queuing uses both the low-priority and high-priority queues. If the value is 1 (true), queued statements always go to the high-priority queue.
This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”
thread_pool_max_unused_threadsIntroduced 5.7.9 Command-Line Format --thread_pool_max_unused_threads=#System Variable Name thread_pool_max_unused_threadsVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 0Min Value 0Max Value 4096The maximum permitted number of unused threads in the thread pool. This variable makes it possible to limit the amount of memory used by sleeping threads.
A value of 0 (the default) means no limit on the number of sleeping threads. A value of
NwhereNis greater than 0 means 1 consumer thread andN−1 reserve threads. In this case, if a thread is ready to sleep but the number of sleeping threads is already at the maximum, the thread exits rather than going to sleep.A sleeping thread is either sleeping as a consumer thread or a reserve thread. The thread pool permits one thread to be the consumer thread when sleeping. If a thread goes to sleep and there is no existing consumer thread, it will sleep as a consumer thread. When a thread must be woken up, a consumer thread is selected if there is one. A reserve thread is selected only when there is no consumer thread to wake up.
This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”
-
Introduced 5.7.9 Command-Line Format --thread_pool_prio_kickup_timer=#System Variable Name thread_pool_prio_kickup_timerVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 1000Min Value 0Max Value 4294967294This variable affects statements waiting for execution in the low-priority queue. The value is the number of milliseconds before a waiting statement is moved to the high-priority queue. The default is 1000 (1 second). The range of values is 0 to 232 − 2.
This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”
-
Introduced 5.7.9 Command-Line Format --thread_pool_size=#System Variable Name thread_pool_sizeVariable Scope Global Dynamic Variable No Permitted Values Type integerDefault 16Min Value 1Max Value 64The number of thread groups in the thread pool. This is the most important parameter controlling thread pool performance. It affects how many statements can execute simultaneously. The default value is 16, with a range from 1 to 64 of permissible values. If a value outside this range is specified, the thread pool plugin does not load and the server writes a message to the error log.
This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”
-
Introduced 5.7.9 Command-Line Format --thread_pool_stall_limit=#System Variable Name thread_pool_stall_limitVariable Scope Global Dynamic Variable Yes Permitted Values Type integerDefault 6Min Value 4Max Value 600This variable affects executing statements. The value is the amount of time a statement has to finish after starting to execute before it becomes defined as stalled, at which point the thread pool permits the thread group to begin executing another statement. The value is measured in 10 millisecond units, so a value of 6 (the default) means 60ms. The range of values is 4 to 600 (40ms to 6s). Short wait values permit threads to start more quickly. Short values are also better for avoiding deadlock situations. Long wait values are useful for workloads that include long-running statements, to avoid starting too many new statements while the current ones execute.
This variable was added in MySQL 5.7.9. It is available only if the thread pool plugin is enabled. See Section 6.5.4, “MySQL Enterprise Thread Pool”
-
Command-Line Format --thread_stack=#System Variable Name thread_stackVariable Scope Global Dynamic Variable No Permitted Values (32-bit platforms) Type integerDefault 196608Min Value 131072Max Value 4294967295Block Size 1024Permitted Values (64-bit platforms) Type integerDefault 262144Min Value 131072Max Value 18446744073709551615Block Size 1024The stack size for each thread. The default of 192KB (256KB for 64-bit systems) is large enough for normal operation. If the thread stack size is too small, it limits the complexity of the SQL statements that the server can handle, the recursion depth of stored procedures, and other memory-consuming actions.
This variable is unused. It is deprecated and will be removed in a future MySQL release.
-
System Variable Name time_zoneVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringThe current time zone. This variable is used to initialize the time zone for each client that connects. By default, the initial value of this is
'SYSTEM'(which means, “use the value ofsystem_time_zone”). The value can be specified explicitly at server startup with the--default-time-zoneoption. See Section 11.6, “MySQL Server Time Zone Support”. -
Deprecated 5.6.20 Removed 5.7.5 Command-Line Format --timed_mutexesSystem Variable Name timed_mutexesVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault OFFThis deprecated variable has no use and was removed in MySQL 5.7.5.
-
System Variable Name timestampVariable Scope Session Dynamic Variable Yes Permitted Values Type numericSet the time for this client. This is used to get the original timestamp if you use the binary log to restore rows.
timestamp_valueshould be a Unix epoch timestamp (a value like that returned byUNIX_TIMESTAMP(), not a value in'YYYY-MM-DD hh:mm:ss'format) orDEFAULT.Setting
timestampto a constant value causes it to retain that value until it is changed again. SettingtimestamptoDEFAULTcauses its value to be the current date and time as of the time it is accessed.In MySQL 5.7,
timestampis aDOUBLErather thanBIGINTbecause its value includes a microseconds part.SET timestampaffects the value returned byNOW()but not bySYSDATE(). This means that timestamp settings in the binary log have no effect on invocations ofSYSDATE(). The server can be started with the--sysdate-is-nowoption to causeSYSDATE()to be an alias forNOW(), in which caseSET timestampaffects both functions. -
Introduced 5.7.10 Command-Line Format --tls_version=protocol_listSystem Variable Name tls_versionVariable Scope Global Dynamic Variable No Permitted Values (OpenSSL) Type stringDefault TLSv1,TLSv1.1,TLSv1.2Permitted Values (yaSSL) Type stringDefault TLSv1,TLSv1.1The protocols permitted by the server for encrypted connections. The value is a comma-separated list containing one or more protocol names. The protocols that can be named for this variable depend on the SSL library used to compile MySQL. For details, see Section 7.4.3, “Secure Connection Protocols and Ciphers”.
-
Command-Line Format --tmp_table_size=#System Variable Name tmp_table_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type integerDefault 16777216Min Value 1024Max Value 18446744073709551615The maximum size of internal in-memory temporary tables. This variable does not apply to user-created
MEMORYtables.The actual limit is determined from whichever of the values of
tmp_table_sizeandmax_heap_table_sizeis smaller. If an in-memory temporary table exceeds the limit, MySQL automatically converts it to an on-disk temporary table. As of MySQL 5.7.5, theinternal_tmp_disk_storage_engineoption defines the storage engine used for on-disk temporary tables. Prior to MySQL 5.7.5, theMyISAMstorage engine is used.Increase the value of
tmp_table_size(andmax_heap_table_sizeif necessary) if you do many advancedGROUP BYqueries and you have lots of memory.You can compare the number of internal on-disk temporary tables created to the total number of internal temporary tables created by comparing the values of the
Created_tmp_disk_tablesandCreated_tmp_tablesvariables.See also Section 9.4.4, “Internal Temporary Table Use in MySQL”.
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Command-Line Format --tmpdir=dir_nameSystem Variable Name tmpdirVariable Scope Global Dynamic Variable No Permitted Values Type directory nameThe directory used for temporary files and temporary tables. This variable can be set to a list of several paths that are used in round-robin fashion. Paths should be separated by colon characters (“
:”) on Unix and semicolon characters (“;”) on Windows.The multiple-directory feature can be used to spread the load between several physical disks. If the MySQL server is acting as a replication slave, you should not set
tmpdirto point to a directory on a memory-based file system or to a directory that is cleared when the server host restarts. A replication slave needs some of its temporary files to survive a machine restart so that it can replicate temporary tables orLOAD DATA INFILEoperations. If files in the temporary file directory are lost when the server restarts, replication fails. You can set the slave's temporary directory using theslave_load_tmpdirvariable. In that case, the slave will not use the generaltmpdirvalue and you can settmpdirto a nonpermanent location. -
Command-Line Format --transaction_alloc_block_size=#System Variable Name transaction_alloc_block_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (>= 5.7.6) Type integerDefault 8192Min Value 1024Max Value 131072Block Size 1024Permitted Values (32-bit platforms, <= 5.7.5) Type integerDefault 8192Min Value 1024Max Value 4294967295Block Size 1024Permitted Values (64-bit platforms, <= 5.7.5) Type integerDefault 8192Min Value 1024Max Value 18446744073709551615Block Size 1024The amount in bytes by which to increase a per-transaction memory pool which needs memory. See the description of
transaction_prealloc_size. -
Command-Line Format --transaction_prealloc_size=#System Variable Name transaction_prealloc_sizeVariable Scope Global, Session Dynamic Variable Yes Permitted Values (>= 5.7.6) Type integerDefault 4096Min Value 1024Max Value 131072Block Size 1024Permitted Values (32-bit platforms, <= 5.7.5) Type integerDefault 4096Min Value 1024Max Value 4294967295Block Size 1024Permitted Values (64-bit platforms, <= 5.7.5) Type integerDefault 4096Min Value 1024Max Value 18446744073709551615Block Size 1024There is a per-transaction memory pool from which various transaction-related allocations take memory. The initial size of the pool in bytes is
transaction_prealloc_size. For every allocation that cannot be satisfied from the pool because it has insufficient memory available, the pool is increased bytransaction_alloc_block_sizebytes. When the transaction ends, the pool is truncated totransaction_prealloc_sizebytes.By making
transaction_prealloc_sizesufficiently large to contain all statements within a single transaction, you can avoid manymalloc()calls. transaction_write_set_extractionIntroduced 5.7.6 Command-Line Format --transaction_write_set_extraction=[value]System Variable Name transaction_write_set_extractionVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type enumerationDefault OFFValid Values OFFMURMUR32Reserved for future use.
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System Variable Name tx_isolationVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type enumerationDefault REPEATABLE-READValid Values READ-UNCOMMITTEDREAD-COMMITTEDREPEATABLE-READSERIALIZABLEThe default transaction isolation level. Defaults to
REPEATABLE-READ.This variable can be set directly, or indirectly using the
SET TRANSACTIONstatement. See Section 14.3.6, “SET TRANSACTION Syntax”. If you settx_isolationdirectly to an isolation level name that contains a space, the name should be enclosed within quotation marks, with the space replaced by a dash. For example:SET tx_isolation = 'READ-COMMITTED';
Any unique prefix of a valid value may be used to set the value of this variable.
The default transaction isolation level can also be set at startup using the
--transaction-isolationserver option. -
System Variable Name tx_read_onlyVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault OFFThe default transaction access mode. The value can be
OFF(read/write, the default) orON(read only).This variable can be set directly, or indirectly using the
SET TRANSACTIONstatement. See Section 14.3.6, “SET TRANSACTION Syntax”.To set the default transaction access mode at startup, use the
--transaction-read-onlyserver option. -
System Variable Name unique_checksVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault 1If set to 1 (the default), uniqueness checks for secondary indexes in
InnoDBtables are performed. If set to 0, storage engines are permitted to assume that duplicate keys are not present in input data. If you know for certain that your data does not contain uniqueness violations, you can set this to 0 to speed up large table imports toInnoDB.Setting this variable to 0 does not require storage engines to ignore duplicate keys. An engine is still permitted to check for them and issue duplicate-key errors if it detects them.
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Command-Line Format --updatable_views_with_limit=#System Variable Name updatable_views_with_limitVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type booleanDefault 1This variable controls whether updates to a view can be made when the view does not contain all columns of the primary key defined in the underlying table, if the update statement contains a
LIMITclause. (Such updates often are generated by GUI tools.) An update is anUPDATEorDELETEstatement. Primary key here means aPRIMARY KEY, or aUNIQUEindex in which no column can containNULL.The variable can have two values:
1orYES: Issue a warning only (not an error message). This is the default value.0orNO: Prohibit the update.
validate_password_xxxThe
validate_passwordplugin implements a set of system variables having names of the formvalidate_password_. These variables affect password testing by that plugin; see Section 7.5.2.2, “Password Validation Plugin Options and Variables”.xxx-
System Variable Name validate_user_pluginsVariable Scope Global Dynamic Variable No Permitted Values Type booleanDefault ONIf this variable is enabled (the default), the server checks each user account and produces a warning if conditions are found that would make the account unusable:
The account requires an authentication plugin that is not loaded.
The account requires the
sha256_passwordauthentication plugin but the server was started with neither SSL nor RSA enabled as required by this plugin.
Enabling
validate_user_pluginsslows down server initialization andFLUSH PRIVILEGES. If you do not require the additional checking, you can disable this variable at startup to avoid the performance decrement. The version number for the server. The value might also include a suffix indicating server build or configuration information.
-logindicates that one or more of the general log, slow query log, or binary log are enabled.-debugindicates that the server was built with debugging support enabled.-
System Variable Name version_commentVariable Scope Global Dynamic Variable No Permitted Values Type stringThe CMake configuration program has a
COMPILATION_COMMENToption that permits a comment to be specified when building MySQL. This variable contains the value of that comment. See Section 2.9.4, “MySQL Source-Configuration Options”. -
System Variable Name version_compile_machineVariable Scope Global Dynamic Variable No Permitted Values Type stringThe type of the server binary.
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System Variable Name version_compile_osVariable Scope Global Dynamic Variable No Permitted Values Type stringThe type of operating system on which MySQL was built.
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Command-Line Format --wait_timeout=#System Variable Name wait_timeoutVariable Scope Global, Session Dynamic Variable Yes Permitted Values (Windows) Type integerDefault 28800Min Value 1Max Value 2147483Permitted Values (Other) Type integerDefault 28800Min Value 1Max Value 31536000The number of seconds the server waits for activity on a noninteractive connection before closing it.
On thread startup, the session
wait_timeoutvalue is initialized from the globalwait_timeoutvalue or from the globalinteractive_timeoutvalue, depending on the type of client (as defined by theCLIENT_INTERACTIVEconnect option tomysql_real_connect()). See alsointeractive_timeout. The number of errors, warnings, and notes that resulted from the last statement that generated messages. This variable is read only. See Section 14.7.5.40, “SHOW WARNINGS Syntax”.
The MySQL server maintains many system variables that indicate how
it is configured. Section 6.1.4, “Server System Variables”,
describes the meaning of these variables. Each system variable has
a default value. System variables can be set at server startup
using options on the command line or in an option file. Most of
them can be changed dynamically while the server is running by
means of the
SET
statement, which enables you to modify operation of the server
without having to stop and restart it. You can refer to system
variable values in expressions.
The server maintains two kinds of system variables. Global variables affect the overall operation of the server. Session variables affect its operation for individual client connections. A given system variable can have both a global and a session value. Global and session system variables are related as follows:
When the server starts, it initializes all global variables to their default values. These defaults can be changed by options specified on the command line or in an option file. (See Section 5.2.3, “Specifying Program Options”.)
The server also maintains a set of session variables for each client that connects. The client's session variables are initialized at connect time using the current values of the corresponding global variables. For example, the client's SQL mode is controlled by the session
sql_modevalue, which is initialized when the client connects to the value of the globalsql_modevalue.
System variable values can be set globally at server startup by
using options on the command line or in an option file. When you
use a startup option to set a variable that takes a numeric value,
the value can be given with a suffix of K,
M, or G (either uppercase or
lowercase) to indicate a multiplier of 1024,
10242 or
10243; that is, units of kilobytes,
megabytes, or gigabytes, respectively. Thus, the following command
starts the server with a query cache size of 16 megabytes and a
maximum packet size of one gigabyte:
mysqld --query_cache_size=16M --max_allowed_packet=1G
Within an option file, those variables are set like this:
[mysqld] query_cache_size=16M max_allowed_packet=1G
The lettercase of suffix letters does not matter;
16M and 16m are equivalent,
as are 1G and 1g.
If you want to restrict the maximum value to which a system
variable can be set at runtime with the
SET
statement, you can specify this maximum by using an option of the
form
--maximum-
at server startup. For example, to prevent the value of
var_name=valuequery_cache_size from being
increased to more than 32MB at runtime, use the option
--maximum-query_cache_size=32M.
Many system variables are dynamic and can be changed while the
server runs by using the
SET
statement. For a list, see
Section 6.1.5.2, “Dynamic System Variables”. To change a system
variable with
SET,
refer to it as var_name, optionally
preceded by a modifier:
To indicate explicitly that a variable is a global variable, precede its name by
GLOBALor@@global.. TheSUPERprivilege is required to set global variables.To indicate explicitly that a variable is a session variable, precede its name by
SESSION,@@session., or@@. Setting a session variable requires no special privilege, but a client can change only its own session variables, not those of any other client.LOCALand@@local.are synonyms forSESSIONand@@session..If no modifier is present,
SETchanges the session variable.
A SET
statement can contain multiple variable assignments, separated by
commas. If you set several system variables, the most recent
GLOBAL or SESSION modifier
in the statement is used for following variables that have no
modifier specified.
Examples:
SET sort_buffer_size=10000; SET @@local.sort_buffer_size=10000; SET GLOBAL sort_buffer_size=1000000, SESSION sort_buffer_size=1000000; SET @@sort_buffer_size=1000000; SET @@global.sort_buffer_size=1000000, @@local.sort_buffer_size=1000000;
The @@
syntax for system variables is supported for compatibility with
some other database systems.
var_name
If you change a session system variable, the value remains in effect until your session ends or until you change the variable to a different value. The change is not visible to other clients.
If you change a global system variable, the value is remembered
and used for new connections until the server restarts. (To make a
global system variable setting permanent, you should set it in an
option file.) The change is visible to any client that accesses
that global variable. However, the change affects the
corresponding session variable only for clients that connect after
the change. The global variable change does not affect the session
variable for any client that is currently connected (not even that
of the client that issues the
SET
GLOBAL statement).
To prevent incorrect usage, MySQL produces an error if you use
SET
GLOBAL with a variable that can only be used with
SET
SESSION or if you do not specify
GLOBAL (or @@global.) when
setting a global variable.
To set a SESSION variable to the
GLOBAL value or a GLOBAL
value to the compiled-in MySQL default value (or autosized
default, for those variables that are autosized), use the
DEFAULT keyword. For example, the following two
statements are identical in setting the session value of
max_join_size to the global
value:
SET max_join_size=DEFAULT; SET @@session.max_join_size=@@global.max_join_size;
Not all system variables can be set to DEFAULT.
In such cases, use of DEFAULT results in an
error.
You can refer to the values of specific global or session system
variables in expressions by using one of the
@@-modifiers. For example, you can retrieve
values in a SELECT statement like
this:
SELECT @@global.sql_mode, @@session.sql_mode, @@sql_mode;
When you refer to a system variable in an expression as
@@ (that is,
when you do not specify var_name@@global. or
@@session.), MySQL returns the session value if
it exists and the global value otherwise. (This differs from
SET @@, which always refers to
the session value.)
var_name =
value
Some variables displayed by SHOW VARIABLES
may not be available using SELECT
@@ syntax; an
var_nameUnknown system variable occurs. As a
workaround in such cases, you can use SHOW VARIABLES
LIKE '.
var_name'
Suffixes for specifying a value multiplier can be used when
setting a variable at server startup, but not to set the value
with SET
at runtime. On the other hand, with
SET you
can assign a variable's value using an expression, which is not
true when you set a variable at server startup. For example, the
first of the following lines is legal at server startup, but the
second is not:
shell>mysql --max_allowed_packet=16Mshell>mysql --max_allowed_packet=16*1024*1024
Conversely, the second of the following lines is legal at runtime, but the first is not:
mysql>SET GLOBAL max_allowed_packet=16M;mysql>SET GLOBAL max_allowed_packet=16*1024*1024;
Some system variables can be enabled with the
SET
statement by setting them to ON or
1, or disabled by setting them to
OFF or 0. However, to set
such a variable on the command line or in an option file, you
must set it to 1 or 0;
setting it to ON or OFF
will not work. For example, on the command line,
--delay_key_write=1 works but
--delay_key_write=ON does not.
To display system variable names and values, use the
SHOW VARIABLES statement:
mysql> SHOW VARIABLES;
+---------------------------------+-----------------------------------+
| Variable_name | Value |
+---------------------------------+-----------------------------------+
| auto_increment_increment | 1 |
| auto_increment_offset | 1 |
| automatic_sp_privileges | ON |
| back_log | 50 |
| basedir | /home/mysql/ |
| binlog_cache_size | 32768 |
| bulk_insert_buffer_size | 8388608 |
| character_set_client | latin1 |
| character_set_connection | latin1 |
| character_set_database | latin1 |
| character_set_results | latin1 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /home/mysql/share/mysql/charsets/ |
| collation_connection | latin1_swedish_ci |
| collation_database | latin1_swedish_ci |
| collation_server | latin1_swedish_ci |
...
| innodb_autoextend_increment | 8 |
| innodb_buffer_pool_size | 8388608 |
| innodb_checksums | ON |
| innodb_commit_concurrency | 0 |
| innodb_concurrency_tickets | 500 |
| innodb_data_file_path | ibdata1:10M:autoextend |
| innodb_data_home_dir | |
...
| version | 5.1.6-alpha-log |
| version_comment | Source distribution |
| version_compile_machine | i686 |
| version_compile_os | suse-linux |
| wait_timeout | 28800 |
+---------------------------------+-----------------------------------+
With a LIKE clause, the statement
displays only those variables that match the pattern. To obtain a
specific variable name, use a LIKE
clause as shown:
SHOW VARIABLES LIKE 'max_join_size'; SHOW SESSION VARIABLES LIKE 'max_join_size';
To get a list of variables whose name match a pattern, use the
“%” wildcard character in a
LIKE clause:
SHOW VARIABLES LIKE '%size%'; SHOW GLOBAL VARIABLES LIKE '%size%';
Wildcard characters can be used in any position within the pattern
to be matched. Strictly speaking, because
“_” is a wildcard that matches any
single character, you should escape it as
“\_” to match it literally. In
practice, this is rarely necessary.
For SHOW VARIABLES, if you specify
neither GLOBAL nor SESSION,
MySQL returns SESSION values.
The reason for requiring the GLOBAL keyword
when setting GLOBAL-only variables but not when
retrieving them is to prevent problems in the future. If we were
to remove a SESSION variable that has the same
name as a GLOBAL variable, a client with the
SUPER privilege might accidentally
change the GLOBAL variable rather than just the
SESSION variable for its own connection. If we
add a SESSION variable with the same name as a
GLOBAL variable, a client that intends to
change the GLOBAL variable might find only its
own SESSION variable changed.
A structured variable differs from a regular system variable in two respects:
Its value is a structure with components that specify server parameters considered to be closely related.
There might be several instances of a given type of structured variable. Each one has a different name and refers to a different resource maintained by the server.
MySQL supports one structured variable type, which specifies parameters governing the operation of key caches. A key cache structured variable has these components:
This section describes the syntax for referring to structured variables. Key cache variables are used for syntax examples, but specific details about how key caches operate are found elsewhere, in Section 9.10.2, “The MyISAM Key Cache”.
To refer to a component of a structured variable instance, you
can use a compound name in
instance_name.component_name format.
Examples:
hot_cache.key_buffer_size hot_cache.key_cache_block_size cold_cache.key_cache_block_size
For each structured system variable, an instance with the name
of default is always predefined. If you refer
to a component of a structured variable without any instance
name, the default instance is used. Thus,
default.key_buffer_size and
key_buffer_size both refer to
the same system variable.
Structured variable instances and components follow these naming rules:
For a given type of structured variable, each instance must have a name that is unique within variables of that type. However, instance names need not be unique across structured variable types. For example, each structured variable has an instance named
default, sodefaultis not unique across variable types.The names of the components of each structured variable type must be unique across all system variable names. If this were not true (that is, if two different types of structured variables could share component member names), it would not be clear which default structured variable to use for references to member names that are not qualified by an instance name.
If a structured variable instance name is not legal as an unquoted identifier, refer to it as a quoted identifier using backticks. For example,
hot-cacheis not legal, but`hot-cache`is.global,session, andlocalare not legal instance names. This avoids a conflict with notation such as@@global.for referring to nonstructured system variables.var_name
Currently, the first two rules have no possibility of being violated because the only structured variable type is the one for key caches. These rules will assume greater significance if some other type of structured variable is created in the future.
With one exception, you can refer to structured variable components using compound names in any context where simple variable names can occur. For example, you can assign a value to a structured variable using a command-line option:
shell> mysqld --hot_cache.key_buffer_size=64K
In an option file, use this syntax:
[mysqld] hot_cache.key_buffer_size=64K
If you start the server with this option, it creates a key cache
named hot_cache with a size of 64KB in
addition to the default key cache that has a default size of
8MB.
Suppose that you start the server as follows:
shell>mysqld --key_buffer_size=256K \--extra_cache.key_buffer_size=128K \--extra_cache.key_cache_block_size=2048
In this case, the server sets the size of the default key cache
to 256KB. (You could also have written
--default.key_buffer_size=256K.) In addition,
the server creates a second key cache named
extra_cache that has a size of 128KB, with
the size of block buffers for caching table index blocks set to
2048 bytes.
The following example starts the server with three different key caches having sizes in a 3:1:1 ratio:
shell>mysqld --key_buffer_size=6M \--hot_cache.key_buffer_size=2M \--cold_cache.key_buffer_size=2M
Structured variable values may be set and retrieved at runtime
as well. For example, to set a key cache named
hot_cache to a size of 10MB, use either of
these statements:
mysql>SET GLOBAL hot_cache.key_buffer_size = 10*1024*1024;mysql>SET @@global.hot_cache.key_buffer_size = 10*1024*1024;
To retrieve the cache size, do this:
mysql> SELECT @@global.hot_cache.key_buffer_size;
However, the following statement does not work. The variable is
not interpreted as a compound name, but as a simple string for a
LIKE pattern-matching operation:
mysql> SHOW GLOBAL VARIABLES LIKE 'hot_cache.key_buffer_size';
This is the exception to being able to use structured variable names anywhere a simple variable name may occur.
Many server system variables are dynamic and can be set at
runtime using SET
GLOBAL or
SET
SESSION. You can also obtain their values using
SELECT. See
Section 6.1.5, “Using System Variables”.
The following table shows the full list of all dynamic system
variables. The last column indicates for each variable whether
GLOBAL or SESSION (or
both) apply. The table also lists session options that can be
set with the
SET
statement. Section 6.1.4, “Server System Variables”, discusses
these options.
Variables that have a type of “string” take a
string value. Variables that have a type of
“numeric” take a numeric value. Variables that have
a type of “boolean” can be set to 0, 1,
ON or OFF. (If you set
them on the command line or in an option file, use the numeric
values.) Variables that are marked as “enumeration”
normally should be set to one of the available values for the
variable, but can also be set to the number that corresponds to
the desired enumeration value. For enumerated system variables,
the first enumeration value corresponds to 0. This differs from
ENUM columns, for which the first
enumeration value corresponds to 1.
Table 6.3 Dynamic Variable Summary
The MySQL server maintains many status variables that provide
information about its operation. You can view these variables and
their values by using the SHOW [GLOBAL | SESSION]
STATUS statement (see Section 14.7.5.35, “SHOW STATUS Syntax”).
The optional GLOBAL keyword aggregates the
values over all connections, and SESSION shows
the values for the current connection.
mysql> SHOW GLOBAL STATUS;
+-----------------------------------+------------+
| Variable_name | Value |
+-----------------------------------+------------+
| Aborted_clients | 0 |
| Aborted_connects | 0 |
| Bytes_received | 155372598 |
| Bytes_sent | 1176560426 |
...
| Connections | 30023 |
| Created_tmp_disk_tables | 0 |
| Created_tmp_files | 3 |
| Created_tmp_tables | 2 |
...
| Threads_created | 217 |
| Threads_running | 88 |
| Uptime | 1389872 |
+-----------------------------------+------------+
Several status variables provide statement counts. To determine the number of statements executed, use these relationships:
SUM(Com_xxx) + Qcache_hits = Questions + statements executed within stored programs = Queries
Many status variables are reset to 0 by the
FLUSH STATUS
statement.
The following table lists all available server status variables:
Table 6.4 Status Variable Summary
The status variables have the meanings shown in the following list. For meanings of status variables specific to MySQL Cluster, see Section 19.3.3.8.3, “MySQL Cluster Status Variables”.
The number of connections that were aborted because the client died without closing the connection properly. See Section B.5.2.11, “Communication Errors and Aborted Connections”.
The number of failed attempts to connect to the MySQL server. See Section B.5.2.11, “Communication Errors and Aborted Connections”.
For additional connection-related information, check the
Connection_errors_status variables and thexxxhost_cachetable.As of MySQL 5.7.3,
Aborted_connectsis not visible in the embedded server because for that server it is not updated and is not meaningful.The number of transactions that used the temporary binary log cache but that exceeded the value of
binlog_cache_sizeand used a temporary file to store statements from the transaction.The number of nontransactional statements that caused the binary log transaction cache to be written to disk is tracked separately in the
Binlog_stmt_cache_disk_usestatus variable.The number of transactions that used the binary log cache.
The number of nontransaction statements that used the binary log statement cache but that exceeded the value of
binlog_stmt_cache_sizeand used a temporary file to store those statements.The number of nontransactional statements that used the binary log statement cache.
The number of bytes received from all clients.
The number of bytes sent to all clients.
The
Com_statement counter variables indicate the number of times eachxxxxxxstatement has been executed. There is one status variable for each type of statement. For example,Com_deleteandCom_updatecountDELETEandUPDATEstatements, respectively.Com_delete_multiandCom_update_multiare similar but apply toDELETEandUPDATEstatements that use multiple-table syntax.If a query result is returned from query cache, the server increments the
Qcache_hitsstatus variable, notCom_select. See Section 9.10.3.4, “Query Cache Status and Maintenance”.The discussion at the beginning of this section indicates how to relate these statement-counting status variables to other such variables.
All of the
Com_stmt_variables are increased even if a prepared statement argument is unknown or an error occurred during execution. In other words, their values correspond to the number of requests issued, not to the number of requests successfully completed.xxxThe
Com_stmt_status variables are as follows:xxxCom_stmt_prepareCom_stmt_executeCom_stmt_fetchCom_stmt_send_long_dataCom_stmt_resetCom_stmt_close
Those variables stand for prepared statement commands. Their names refer to the
COM_command set used in the network layer. In other words, their values increase whenever prepared statement API calls such as mysql_stmt_prepare(), mysql_stmt_execute(), and so forth are executed. However,xxxCom_stmt_prepare,Com_stmt_executeandCom_stmt_closealso increase forPREPARE,EXECUTE, orDEALLOCATE PREPARE, respectively. Additionally, the values of the older statement counter variablesCom_prepare_sql,Com_execute_sql, andCom_dealloc_sqlincrease for thePREPARE,EXECUTE, andDEALLOCATE PREPAREstatements.Com_stmt_fetchstands for the total number of network round-trips issued when fetching from cursors.Com_stmt_reprepareindicates the number of times statements were automatically reprepared by the server after metadata changes to tables or views referred to by the statement. A reprepare operation incrementsCom_stmt_reprepare, and alsoCom_stmt_prepare.Com_explain_otherindicates the number ofEXPLAIN FOR CONNECTIONstatements executed. See Section 9.8.4, “Obtaining Execution Plan Information for a Named Connection”. It was introduced in MySQL 5.7.2.Com_change_repl_filterindicates the number ofCHANGE REPLICATION FILTERstatements executed. It was introduced in MySQL 5.7.3.Whether the client connection uses compression in the client/server protocol.
These variables provide information about errors that occur during the client connection process. They are global only and represent error counts aggregated across connections from all hosts. These variables track errors not accounted for by the host cache (see Section 9.12.6.2, “DNS Lookup Optimization and the Host Cache”), such as errors that are not associated with TCP connections, occur very early in the connection process (even before an IP address is known), or are not specific to any particular IP address (such as out-of-memory conditions).
As of MySQL 5.7.3, the
Connection_errors_status variables are not visible in the embedded server because for that server they are not updated and are not meaningful.xxxThe number of errors that occurred during calls to
accept()on the listening port.The number of connections refused due to internal errors in the server, such as failure to start a new thread or an out-of-memory condition.
Connection_errors_max_connectionsThe number of connections refused because the server
max_connectionslimit was reached.The number of errors that occurred while searching for connecting client IP addresses.
The number of errors that occurred during calls to
select()orpoll()on the listening port. (Failure of this operation does not necessarily means a client connection was rejected.)The number of connections refused by the
libwraplibrary.
The number of connection attempts (successful or not) to the MySQL server.
The number of internal on-disk temporary tables created by the server while executing statements.
If an internal temporary table is created initially as an in-memory table but becomes too large, MySQL automatically converts it to an on-disk table. The maximum size for in-memory temporary tables is the minimum of the
tmp_table_sizeandmax_heap_table_sizevalues. IfCreated_tmp_disk_tablesis large, you may want to increase thetmp_table_sizeormax_heap_table_sizevalue to lessen the likelihood that internal temporary tables in memory will be converted to on-disk tables.You can compare the number of internal on-disk temporary tables created to the total number of internal temporary tables created by comparing the values of the
Created_tmp_disk_tablesandCreated_tmp_tablesvariables.See also Section 9.4.4, “Internal Temporary Table Use in MySQL”.
How many temporary files mysqld has created.
The number of internal temporary tables created by the server while executing statements.
You can compare the number of internal on-disk temporary tables created to the total number of internal temporary tables created by comparing the values of the
Created_tmp_disk_tablesandCreated_tmp_tablesvariables.See also Section 9.4.4, “Internal Temporary Table Use in MySQL”.
Each invocation of the
SHOW STATUSstatement uses an internal temporary table and increments the globalCreated_tmp_tablesvalue.This status variable is deprecated (because
DELAYEDinserts are not supported), and will be removed in a future release.This status variable is deprecated (because
DELAYEDinserts are not supported), and will be removed in a future release.This status variable is deprecated (because
DELAYEDinserts are not supported), and will be removed in a future release.The number of times the server flushes tables, whether because a user executed a
FLUSH TABLESstatement or due to internal server operation. It is also incremented by receipt of aCOM_REFRESHpacket. This is in contrast toCom_flush, which indicates how manyFLUSHstatements have been executed, whetherFLUSH TABLES,FLUSH LOGS, and so forth.The number of internal
COMMITstatements.The number of times that rows have been deleted from tables.
The server increments this variable for each call to its
external_lock()function, which generally occurs at the beginning and end of access to a table instance. There might be differences among storage engines. This variable can be used, for example, to discover for a statement that accesses a partitioned table how many partitions were pruned before locking occurred: Check how much the counter increased for the statement, subtract 2 (2 calls for the table itself), then divide by 2 to get the number of partitions locked.The number of times the server uses a storage engine's own Multi-Range Read implementation for table access.
A counter for the prepare phase of two-phase commit operations.
The number of times the first entry in an index was read. If this value is high, it suggests that the server is doing a lot of full index scans; for example,
SELECT col1 FROM foo, assuming thatcol1is indexed.The number of requests to read a row based on a key. If this value is high, it is a good indication that your tables are properly indexed for your queries.
The number of requests to read the last key in an index. With
ORDER BY, the server will issue a first-key request followed by several next-key requests, whereas withORDER BY DESC, the server will issue a last-key request followed by several previous-key requests.The number of requests to read the next row in key order. This value is incremented if you are querying an index column with a range constraint or if you are doing an index scan.
The number of requests to read the previous row in key order. This read method is mainly used to optimize
ORDER BY ... DESC.The number of requests to read a row based on a fixed position. This value is high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan entire tables or you have joins that do not use keys properly.
The number of requests to read the next row in the data file. This value is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.
The number of requests for a storage engine to perform a rollback operation.
The number of requests for a storage engine to place a savepoint.
The number of requests for a storage engine to roll back to a savepoint.
The number of requests to update a row in a table.
The number of requests to insert a row in a table.
The total number of available
InnoDBundo logs. Supplements theinnodb_undo_logssystem variable, which reports the number of active undo logs.One undo log always resides in the system tablespace, and as of MySQL 5.7.2, 32 undo logs are reserved for use by temporary tables and are hosted in the temporary tablespace (
ibtmp1). See Section 15.4.12.1, “InnoDB Temporary Table Undo Logs”.If you initiate a MySQL instance with 32 or fewer undo logs,
InnoDBstill assigns one undo log to the system tablespace and 32 undo logs to the temporary tablespace. In this case,Innodb_available_undo_logsreports 33 available undo logs even though the instance was initialized with a lesserinnodb_undo_logsvalue.Innodb_buffer_pool_dump_statusThe progress of an operation to record the pages held in the
InnoDBbuffer pool, triggered by the setting ofinnodb_buffer_pool_dump_at_shutdownorinnodb_buffer_pool_dump_now.For related information and examples, see Section 15.6.3.8, “Saving and Restoring the Buffer Pool State”.
Innodb_buffer_pool_load_statusThe progress of an operation to warm up the
InnoDBbuffer pool by reading in a set of pages corresponding to an earlier point in time, triggered by the setting ofinnodb_buffer_pool_load_at_startuporinnodb_buffer_pool_load_now. If the operation introduces too much overhead, you can cancel it by settinginnodb_buffer_pool_load_abort.For related information and examples, see Section 15.6.3.8, “Saving and Restoring the Buffer Pool State”.
The total number of bytes in the
InnoDBbuffer pool containing data. The number includes both dirty and clean pages. For more accurate memory usage calculations than withInnodb_buffer_pool_pages_data, when compressed tables cause the buffer pool to hold pages of different sizes.The number of pages in the
InnoDBbuffer pool containing data. The number includes both dirty and clean pages. When using compressed tables, the reportedInnodb_buffer_pool_pages_datavalue may be larger thanInnodb_buffer_pool_pages_total(Bug #59550).Innodb_buffer_pool_bytes_dirtyThe total current number of bytes held in dirty pages in the
InnoDBbuffer pool. For more accurate memory usage calculations than withInnodb_buffer_pool_pages_dirty, when compressed tables cause the buffer pool to hold pages of different sizes.Innodb_buffer_pool_pages_dirtyThe current number of dirty pages in the
InnoDBbuffer pool.Innodb_buffer_pool_pages_flushedThe number of requests to flush pages from the
InnoDBbuffer pool.The number of free pages in the
InnoDBbuffer pool.Innodb_buffer_pool_pages_latchedThe number of latched pages in the
InnoDBbuffer pool. These are pages currently being read or written, or that cannot be flushed or removed for some other reason. Calculation of this variable is expensive, so it is available only when theUNIV_DEBUGsystem is defined at server build time.The number of pages in the
InnoDBbuffer pool that are busy because they have been allocated for administrative overhead, such as row locks or the adaptive hash index. This value can also be calculated asInnodb_buffer_pool_pages_total−Innodb_buffer_pool_pages_free−Innodb_buffer_pool_pages_data. When using compressed tables,Innodb_buffer_pool_pages_miscmay report an out-of-bounds value (Bug #59550).Innodb_buffer_pool_pages_totalThe total size of the
InnoDBbuffer pool, in pages. When using compressed tables, the reportedInnodb_buffer_pool_pages_datavalue may be larger thanInnodb_buffer_pool_pages_total(Bug #59550)The number of pages read into the
InnoDBbuffer pool by the read-ahead background thread.Innodb_buffer_pool_read_ahead_evictedThe number of pages read into the
InnoDBbuffer pool by the read-ahead background thread that were subsequently evicted without having been accessed by queries.Innodb_buffer_pool_read_ahead_rndThe number of “random” read-aheads initiated by
InnoDB. This happens when a query scans a large portion of a table but in random order.Innodb_buffer_pool_read_requestsThe number of logical read requests.
The number of logical reads that
InnoDBcould not satisfy from the buffer pool, and had to read directly from disk.Innodb_buffer_pool_resize_statusThe status of an operation to resize the
InnoDBbuffer pool dynamically, triggered by setting theinnodb_buffer_pool_sizeparameter dynamically. As of MySQL 5.7.5, theinnodb_buffer_pool_sizeparameter is dynamic, which allows you to resize the buffer pool without restarting the server. See Configuring InnoDB Buffer Pool Size Online for related information.Normally, writes to the
InnoDBbuffer pool happen in the background. WhenInnoDBneeds to read or create a page and no clean pages are available,InnoDBflushes some dirty pages first and waits for that operation to finish. This counter counts instances of these waits. Ifinnodb_buffer_pool_sizehas been set properly, this value should be small.Innodb_buffer_pool_write_requestsThe number of writes done to the
InnoDBbuffer pool.The number of
fsync()operations so far. The frequency offsync()calls is influenced by the setting of theinnodb_flush_methodconfiguration option.The current number of pending
fsync()operations. The frequency offsync()calls is influenced by the setting of theinnodb_flush_methodconfiguration option.The current number of pending reads.
The current number of pending writes.
The amount of data read since the server was started (in bytes).
The total number of data reads (OS file reads).
The total number of data writes.
The amount of data written so far, in bytes.
The number of pages that have been written to the doublewrite buffer. See Section 15.12.1, “InnoDB Disk I/O”.
The number of doublewrite operations that have been performed. See Section 15.12.1, “InnoDB Disk I/O”.
Indicates whether the server was built with atomic instructions.
The number of times that the log buffer was too small and a wait was required for it to be flushed before continuing.
The number of write requests for the
InnoDBredo log.The number of physical writes to the
InnoDBredo log file.The number of files
InnoDBcurrently holds open.The number of
fsync()writes done to theInnoDBredo log files.The number of pending
fsync()operations for theInnoDBredo log files.The number of pending writes to the
InnoDBredo log files.The number of bytes written to the
InnoDBredo log files.InnoDBpage size (default 16KB). Many values are counted in pages; the page size enables them to be easily converted to bytes.The number of pages created by operations on
InnoDBtables.The number of pages read from the
InnoDBbuffer pool by operations onInnoDBtables.The number of pages written by operations on
InnoDBtables.The number of row locks currently being waited for by operations on
InnoDBtables.The total time spent in acquiring row locks for
InnoDBtables, in milliseconds.The average time to acquire a row lock for
InnoDBtables, in milliseconds.The maximum time to acquire a row lock for
InnoDBtables, in milliseconds.The number of times operations on
InnoDBtables had to wait for a row lock.The number of rows deleted from
InnoDBtables.The number of rows inserted into
InnoDBtables.The number of rows read from
InnoDBtables.The number of rows updated in
InnoDBtables.Innodb_truncated_status_writesThe number of times output from the
SHOW ENGINE INNODB STATUSstatement has been truncated.The number of key blocks in the
MyISAMkey cache that have changed but have not yet been flushed to disk.The number of unused blocks in the
MyISAMkey cache. You can use this value to determine how much of the key cache is in use; see the discussion ofkey_buffer_sizein Section 6.1.4, “Server System Variables”.The number of used blocks in the
MyISAMkey cache. This value is a high-water mark that indicates the maximum number of blocks that have ever been in use at one time.The number of requests to read a key block from the
MyISAMkey cache.The number of physical reads of a key block from disk into the
MyISAMkey cache. IfKey_readsis large, then yourkey_buffer_sizevalue is probably too small. The cache miss rate can be calculated asKey_reads/Key_read_requests.The number of requests to write a key block to the
MyISAMkey cache.The number of physical writes of a key block from the
MyISAMkey cache to disk.The total cost of the last compiled query as computed by the query optimizer. This is useful for comparing the cost of different query plans for the same query. The default value of 0 means that no query has been compiled yet. The default value is 0.
Last_query_costhas session scope.The
Last_query_costvalue can be computed accurately only for simple “flat” queries, not complex queries such as those with subqueries orUNION. For the latter, the value is set to 0.The number of iterations the query optimizer made in execution plan construction for the previous query.
Last_query_costhas session scope.The number of attempts to connect to locked user accounts. For information about account locking and unlocking, see Section 7.3.10, “User Account Locking”.
This variable was added in MySQL 5.7.6.
The number of
SELECTstatements for which the execution timeout was exceeded. This variable was added in MySQL 5.7.8. Previously, it was namedMax_statement_time_exceeded.The number of
SELECTstatements for which a nonzero execution timeout was set. This includes statements that include a nonzeroMAX_EXECUTION_TIMEoptimizer hint, and statements that include no such hint but execute while the timeout indicated by themax_execution_timesystem variable is nonzero. This variable was added in MySQL 5.7.8. Previously, it was namedMax_statement_time_set.The number of
SELECTstatements for which the attempt to set an execution timeout failed. This variable was added in MySQL 5.7.8. Previously, it was namedMax_statement_time_set_failed.The number of
SELECTstatements for which the execution timeout was exceeded. This variable was added in MySQL 5.7.4 and renamed toMax_execution_time_exceededin MySQL 5.7.8.The number of
SELECTstatements for which a nonzero execution timeout was set. This includes statements that include a nonzeroMAX_STATEMENT_TIMEoption, and statements that include no such option but execute while the timeout indicated by themax_statement_timesystem variable is nonzero. This variable was added in MySQL 5.7.4 and renamed toMax_execution_time_setin MySQL 5.7.8.The number of
SELECTstatements for which the attempt to set an execution timeout failed. This variable was added in MySQL 5.7.4 and renamed toMax_execution_time_set_failedin MySQL 5.7.8.The maximum number of connections that have been in use simultaneously since the server started.
The time at which
Max_used_connectionsreached its current value. This variable was added in MySQL 5.7.5.This status variable is deprecated (because
DELAYEDinserts are not supported), and will be removed in a future release.The character set currently used by the MeCab full-text parser plugin. For related information, see Section 13.9.9, “MeCab Full-Text Parser Plugin”.
Ongoing_anonymous_transaction_countShows the number of ongoing transactions which have been marked as anonymous. This can be used to ensure that no further transactions are waiting to be processed. This variable was added in MySQL 5.7.6.
Ongoing_anonymous_gtid_violating_transaction_countThis status variable is only available in debug builds. Shows the number of ongoing transactions which use
gtid_next=ANONYMOUSand that violate GTID consistency. This variable was added in MySQL 5.7.6.Ongoing_automatic_gtid_violating_transaction_countThis status variable is only available in debug builds. Shows the number of ongoing transactions which use
gtid_next=AUTOMATICand that violate GTID consistency. This variable was added in MySQL 5.7.6.The number of files that are open. This count includes regular files opened by the server. It does not include other types of files such as sockets or pipes. Also, the count does not include files that storage engines open using their own internal functions rather than asking the server level to do so.
The number of streams that are open (used mainly for logging).
The number of cached
.frmfiles.The number of tables that are open.
The number of files that have been opened with
my_open()(amysyslibrary function). Parts of the server that open files without using this function do not increment the count.The number of
.frmfiles that have been cached.The number of tables that have been opened. If
Opened_tablesis big, yourtable_open_cachevalue is probably too small.Performance_schema_xxxPerformance Schema status variables are listed in Section 23.13, “Performance Schema Status Variables”. These variables provide information about instrumentation that could not be loaded or created due to memory constraints.
The current number of prepared statements. (The maximum number of statements is given by the
max_prepared_stmt_countsystem variable.)The number of free memory blocks in the query cache.
The amount of free memory for the query cache.
The number of query cache hits.
The discussion at the beginning of this section indicates how to relate this statement-counting status variable to other such variables.
The number of queries added to the query cache.
The number of queries that were deleted from the query cache because of low memory.
The number of noncached queries (not cacheable, or not cached due to the
query_cache_typesetting).The number of queries registered in the query cache.
The total number of blocks in the query cache.
The number of statements executed by the server. This variable includes statements executed within stored programs, unlike the
Questionsvariable. It does not countCOM_PINGorCOM_STATISTICScommands.The discussion at the beginning of this section indicates how to relate this statement-counting status variable to other such variables.
The number of statements executed by the server. This includes only statements sent to the server by clients and not statements executed within stored programs, unlike the
Queriesvariable. This variable does not countCOM_PING,COM_STATISTICS,COM_STMT_PREPARE,COM_STMT_CLOSE, orCOM_STMT_RESETcommands.The discussion at the beginning of this section indicates how to relate this statement-counting status variable to other such variables.
The number of semisynchronous slaves.
This variable is available only if the master-side semisynchronous replication plugin is installed.
Rpl_semi_sync_master_net_avg_wait_timeThe average time in microseconds the master waited for a slave reply. In MySQL 5.7.4 and later this variable is always
0. In MySQL 5.7.8 and later it is deprecated and it will be removed in a future version.This variable is available only if the master-side semisynchronous replication plugin is installed.
Rpl_semi_sync_master_net_wait_timeThe total time in microseconds the master waited for slave replies. In MySQL 5.7.4 and later this variable is always
0. In MySQL 5.7.8 and later it is deprecated and it will be removed in a future version.This variable is available only if the master-side semisynchronous replication plugin is installed.
Rpl_semi_sync_master_net_waitsThe total number of times the master waited for slave replies.
This variable is available only if the master-side semisynchronous replication plugin is installed.
The number of times the master turned off semisynchronous replication.
This variable is available only if the master-side semisynchronous replication plugin is installed.
The number of commits that were not acknowledged successfully by a slave.
This variable is available only if the master-side semisynchronous replication plugin is installed.
Whether semisynchronous replication currently is operational on the master. The value is
ONif the plugin has been enabled and a commit acknowledgment has occurred. It isOFFif the plugin is not enabled or the master has fallen back to asynchronous replication due to commit acknowledgment timeout.This variable is available only if the master-side semisynchronous replication plugin is installed.
Rpl_semi_sync_master_timefunc_failuresThe number of times the master failed when calling time functions such as
gettimeofday().This variable is available only if the master-side semisynchronous replication plugin is installed.
Rpl_semi_sync_master_tx_avg_wait_timeThe average time in microseconds the master waited for each transaction.
This variable is available only if the master-side semisynchronous replication plugin is installed.
Rpl_semi_sync_master_tx_wait_timeThe total time in microseconds the master waited for transactions.
This variable is available only if the master-side semisynchronous replication plugin is installed.
The total number of times the master waited for transactions.
This variable is available only if the master-side semisynchronous replication plugin is installed.
Rpl_semi_sync_master_wait_pos_backtraverseThe total number of times the master waited for an event with binary coordinates lower than events waited for previously. This can occur when the order in which transactions start waiting for a reply is different from the order in which their binary log events are written.
This variable is available only if the master-side semisynchronous replication plugin is installed.
Rpl_semi_sync_master_wait_sessionsThe number of sessions currently waiting for slave replies.
This variable is available only if the master-side semisynchronous replication plugin is installed.
The number of commits that were acknowledged successfully by a slave.
This variable is available only if the master-side semisynchronous replication plugin is installed.
Whether semisynchronous replication currently is operational on the slave. This is
ONif the plugin has been enabled and the slave I/O thread is running,OFFotherwise.This variable is available only if the slave-side semisynchronous replication plugin is installed.
This variable is available if MySQL was using OpenSSL (see Section 7.4.1, “OpenSSL Versus yaSSL”). Its value is the RSA public key value used by the
sha256_passwordauthentication plugin. The value is nonempty only if the server successfully initializes the private and public keys in the files named by thesha256_password_private_key_pathandsha256_password_public_key_pathsystem variables. The value ofRsa_public_keycomes from the latter file.For information about
sha256_password, see Section 7.5.1.4, “The SHA-256 Authentication Plugin”.The number of joins that perform table scans because they do not use indexes. If this value is not 0, you should carefully check the indexes of your tables.
The number of joins that used a range search on a reference table.
The number of joins that used ranges on the first table. This is normally not a critical issue even if the value is quite large.
The number of joins without keys that check for key usage after each row. If this is not 0, you should carefully check the indexes of your tables.
The number of joins that did a full scan of the first table.
Shows the replication heartbeat interval (in seconds) on a replication slave.
This variable is affected by the value of the
show_compatibility_56system variable. For details, see Effect of show_compatibility_56 on Slave Status Variables.NoteThis variable only shows the status of the default replication channel. To monitor multiple replication channels use the
HEARTBEAT_INTERVALcolumn in thereplication_connection_statustable for the replication channel.Shows when the most recent heartbeat signal was received by a replication slave, as a
TIMESTAMPvalue.This variable is affected by the value of the
show_compatibility_56system variable. For details, see Effect of show_compatibility_56 on Slave Status Variables.NoteThis variable only shows the status of the default replication channel. To monitor multiple replication channels use the
LAST_HEARTBEAT_TIMESTAMPcolumn in thereplication_connection_statustable for the replication channel.The number of temporary tables that the slave SQL thread currently has open. If the value is greater than zero, it is not safe to shut down the slave; see Section 18.4.1.24, “Replication and Temporary Tables”. This variable reports the total count of open temporary tables for all replication channels.
This counter increments with each replication heartbeat received by a replication slave since the last time that the slave was restarted or reset, or a
CHANGE MASTER TOstatement was issued.This variable is affected by the value of the
show_compatibility_56system variable. For details, see Effect of show_compatibility_56 on Slave Status Variables.NoteThis variable only shows the status of the default replication channel. To monitor multiple replication channels use the
COUNT_RECEIVED_HEARTBEATScolumn in thereplication_connection_statustable for the replication channel.The total number of times since startup that the replication slave SQL thread has retried transactions.
This variable is affected by the value of the
show_compatibility_56system variable. For details, see Effect of show_compatibility_56 on Slave Status Variables.NoteThis variable only shows the status of the default replication channel. To monitor multiple replication channels use the
COUNT_TRANSACTIONS_RETRIEScolumn in thereplication_applier_statustable for the replication channel.This is
ONif this server is a replication slave that is connected to a replication master, and both the I/O and SQL threads are running; otherwise, it isOFF.This variable is affected by the value of the
show_compatibility_56system variable. For details, see Effect of show_compatibility_56 on Slave Status Variables.NoteThis variable only shows the status of the default replication channel. To monitor multiple replication channels use the
SERVICE_STATEcolumn in thereplication_applier_statusorreplication_connection_statustables of the replication channel.The number of threads that have taken more than
slow_launch_timeseconds to create.This variable is not meaningful in the embedded server (
libmysqld) and as of MySQL 5.7.2 is no longer visible within the embedded server.The number of queries that have taken more than
long_query_timeseconds. This counter increments regardless of whether the slow query log is enabled. For information about that log, see Section 6.4.5, “The Slow Query Log”.The number of merge passes that the sort algorithm has had to do. If this value is large, you should consider increasing the value of the
sort_buffer_sizesystem variable.The number of sorts that were done using ranges.
The number of sorted rows.
The number of sorts that were done by scanning the table.
The number of negotiates needed to establish the connection.
The number of accepted SSL connections.
The number of callback cache hits.
The current encryption cipher (empty for unencrypted connections).
The list of possible SSL ciphers (empty for non-SSL connections).
The number of SSL connection attempts to an SSL-enabled master.
The number of negotiates needed to establish the connection to an SSL-enabled master.
The SSL context verification depth (how many certificates in the chain are tested).
The SSL context verification mode.
The default SSL timeout.
The number of successful SSL connections to the server.
The number of successful slave connections to an SSL-enabled master.
The last date for which the SSL certificate is valid. To check SSL certificate expiration information, use this statement:
mysql>
SHOW STATUS LIKE 'Ssl_server_not%';+-----------------------+--------------------------+ | Variable_name | Value | +-----------------------+--------------------------+ | Ssl_server_not_after | Apr 28 14:16:39 2025 GMT | | Ssl_server_not_before | May 1 14:16:39 2015 GMT | +-----------------------+--------------------------+The first date for which the SSL certificate is valid.
The number of SSL session cache hits.
The number of SSL session cache misses.
The SSL session cache mode.
The number of SSL session cache overflows.
The SSL session cache size.
The number of SSL session cache timeouts.
How many SSL connections were reused from the cache.
Ssl_used_session_cache_entriesHow many SSL session cache entries were used.
The verification depth for replication SSL connections.
The verification mode for replication SSL connections.
The SSL protocol version of the connection; for example, TLSv1. If the connection is not encrypted, the value is empty.
The number of times that a request for a table lock could be granted immediately.
The number of times that a request for a table lock could not be granted immediately and a wait was needed. If this is high and you have performance problems, you should first optimize your queries, and then either split your table or tables or use replication.
The number of hits for open tables cache lookups.
The number of misses for open tables cache lookups.
The number of overflows for the open tables cache. This is the number of times, after a table is opened or closed, a cache instance has an unused entry and the size of the instance is larger than
table_open_cache/table_open_cache_instances.For the memory-mapped implementation of the log that is used by mysqld when it acts as the transaction coordinator for recovery of internal XA transactions, this variable indicates the largest number of pages used for the log since the server started. If the product of
Tc_log_max_pages_usedandTc_log_page_sizeis always significantly less than the log size, the size is larger than necessary and can be reduced. (The size is set by the--log-tc-sizeoption. This variable is unused: It is unneeded for binary log-based recovery, and the memory-mapped recovery log method is not used unless the number of storage engines that are capable of two-phase commit and that support XA transactions is greater than one. (InnoDBis the only applicable engine.)The page size used for the memory-mapped implementation of the XA recovery log. The default value is determined using
getpagesize(). This variable is unused for the same reasons as described forTc_log_max_pages_used.For the memory-mapped implementation of the recovery log, this variable increments each time the server was not able to commit a transaction and had to wait for a free page in the log. If this value is large, you might want to increase the log size (with the
--log-tc-sizeoption). For binary log-based recovery, this variable increments each time the binary log cannot be closed because there are two-phase commits in progress. (The close operation waits until all such transactions are finished.)The number of threads in the thread cache.
This variable is not meaningful in the embedded server (
libmysqld) and as of MySQL 5.7.2 is no longer visible within the embedded server.The number of currently open connections.
The number of threads created to handle connections. If
Threads_createdis big, you may want to increase thethread_cache_sizevalue. The cache miss rate can be calculated asThreads_created/Connections.The number of threads that are not sleeping.
The number of seconds that the server has been up.
The number of seconds since the most recent
FLUSH STATUSstatement.
The MySQL server can operate in different SQL modes, and can apply
these modes differently for different clients, depending on the
value of the sql_mode system
variable. DBAs can set the global SQL mode to match site server
operating requirements, and each application can set its session
SQL mode to its own requirements.
Modes affect the SQL syntax MySQL supports and the data validation checks it performs. This makes it easier to use MySQL in different environments and to use MySQL together with other database servers.
For answers to questions often asked about server SQL modes in MySQL, see Section A.3, “MySQL 5.7 FAQ: Server SQL Mode”.
When working with InnoDB tables, consider also
the innodb_strict_mode system
variable. It enables additional error checks for
InnoDB tables.
The default SQL mode in MySQL 5.7 includes these
modes: ONLY_FULL_GROUP_BY,
STRICT_TRANS_TABLES,
NO_ZERO_IN_DATE,
NO_ZERO_DATE,
ERROR_FOR_DIVISION_BY_ZERO,
NO_AUTO_CREATE_USER, and
NO_ENGINE_SUBSTITUTION.
The ONLY_FULL_GROUP_BY and
STRICT_TRANS_TABLES modes were
added in MySQL 5.7.5. The
NO_AUTO_CREATE_USER mode was
added in MySQL 5.7.7. The
ERROR_FOR_DIVISION_BY_ZERO,
NO_ZERO_DATE, and
NO_ZERO_IN_DATE modes were
added in MySQL 5.7.8. For additional discussion regarding these
changes to the default SQL mode value, see
SQL Mode Changes in MySQL 5.7.
To set the SQL mode at server startup, use the
--sql-mode="
option on the command line, or
modes"sql-mode="
in an option file such as modes"my.cnf (Unix
operating systems) or my.ini (Windows).
modes is a list of different modes
separated by commas. To clear the SQL mode explicitly, set it to
an empty string using
--sql-mode="" on the command
line, or sql-mode="" in an option
file.
MySQL installation programs may configure the SQL mode during
the installation process. For example,
mysql_install_db creates a default option
file named my.cnf in the base
installation directory. This file contains a line that sets
the SQL mode; see Section 5.4.2, “mysql_install_db — Initialize MySQL Data Directory”.
If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.
To change the SQL mode at runtime, set the global or session
sql_mode system variable using
a SET
statement:
SET GLOBAL sql_mode = 'modes'; SET SESSION sql_mode = 'modes';
Setting the GLOBAL variable requires the
SUPER privilege and affects the
operation of all clients that connect from that time on. Setting
the SESSION variable affects only the current
client. Each client can change its session
sql_mode value at any time.
To determine the current global or session
sql_mode value, use the
following statements:
SELECT @@GLOBAL.sql_mode; SELECT @@SESSION.sql_mode;
SQL mode and user-defined partitioning. Changing the server SQL mode after creating and inserting data into partitioned tables can cause major changes in the behavior of such tables, and could lead to loss or corruption of data. It is strongly recommended that you never change the SQL mode once you have created tables employing user-defined partitioning.
When replicating partitioned tables, differing SQL modes on master and slave can also lead to problems. For best results, you should always use the same server SQL mode on the master and on the slave.
See Section 20.6, “Restrictions and Limitations on Partitioning”, for more information.
The most important sql_mode
values are probably these:
This mode changes syntax and behavior to conform more closely to standard SQL. It is one of the special combination modes listed at the end of this section.
If a value could not be inserted as given into a transactional table, abort the statement. For a nontransactional table, abort the statement if the value occurs in a single-row statement or the first row of a multiple-row statement. More details are given later in this section.
As of MySQL 5.7.5, the default SQL mode includes
STRICT_TRANS_TABLES.Make MySQL behave like a “traditional” SQL database system. A simple description of this mode is “give an error instead of a warning” when inserting an incorrect value into a column. It is one of the special combination modes listed at the end of this section.
When this manual refers to “strict mode,” it means
a mode with either or both
STRICT_TRANS_TABLES or
STRICT_ALL_TABLES enabled.
The following list describes all supported SQL modes:
Do not perform full checking of dates. Check only that the month is in the range from 1 to 12 and the day is in the range from 1 to 31. This is very convenient for Web applications where you obtain year, month, and day in three different fields and you want to store exactly what the user inserted (without date validation). This mode applies to
DATEandDATETIMEcolumns. It does not applyTIMESTAMPcolumns, which always require a valid date.The server requires that month and day values be legal, and not merely in the range 1 to 12 and 1 to 31, respectively. With strict mode disabled, invalid dates such as
'2004-04-31'are converted to'0000-00-00'and a warning is generated. With strict mode enabled, invalid dates generate an error. To permit such dates, enableALLOW_INVALID_DATES.Treat “
"” as an identifier quote character (like the “`” quote character) and not as a string quote character. You can still use “`” to quote identifiers with this mode enabled. WithANSI_QUOTESenabled, you cannot use double quotation marks to quote literal strings, because it is interpreted as an identifier.The
ERROR_FOR_DIVISION_BY_ZEROmode affects handling of division by zero, which includesMOD(. For data-change operations (N,0)INSERT,UPDATE), its effect also depends on whether strict SQL mode is enabled.If this mode is not enabled, division by zero inserts
NULLand produces no warning.If this mode is enabled, division by zero inserts
NULLand produces a warning.If this mode and strict mode are enabled, division by zero produces an error, unless
IGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE, division by zero insertsNULLand produces a warning.
For
SELECT, division by zero returnsNULL. EnablingERROR_FOR_DIVISION_BY_ZEROcauses a warning to be produced as well, regardless of whether strict mode is enabled.As of MySQL 5.7.4,
ERROR_FOR_DIVISION_BY_ZEROis deprecated. In MySQL 5.7.4 through 5.7.7,ERROR_FOR_DIVISION_BY_ZEROdoes nothing when named explicitly. Instead, its effect is included in the effects of strict SQL mode. In MySQL 5.7.8 and later,ERROR_FOR_DIVISION_BY_ZEROdoes have an effect when named explicitly and is not part of strict mode, as before MySQL 5.7.4. However, it should be used in conjunction with strict mode and is enabled by default. A warning occurs ifERROR_FOR_DIVISION_BY_ZEROis enabled without also enabling strict mode or vice versa. For additional discussion, see SQL Mode Changes in MySQL 5.7.Because
ERROR_FOR_DIVISION_BY_ZEROis deprecated, it will be removed in a future MySQL release as a separate mode name and its effect included in the effects of strict SQL mode.The precedence of the
NOToperator is such that expressions such asNOT a BETWEEN b AND care parsed asNOT (a BETWEEN b AND c). In some older versions of MySQL, the expression was parsed as(NOT a) BETWEEN b AND c. The old higher-precedence behavior can be obtained by enabling theHIGH_NOT_PRECEDENCESQL mode.mysql>
SET sql_mode = '';mysql>SELECT NOT 1 BETWEEN -5 AND 5;-> 0 mysql>SET sql_mode = 'HIGH_NOT_PRECEDENCE';mysql>SELECT NOT 1 BETWEEN -5 AND 5;-> 1Permit spaces between a function name and the “
(” character. This causes built-in function names to be treated as reserved words. As a result, identifiers that are the same as function names must be quoted as described in Section 10.2, “Schema Object Names”. For example, because there is aCOUNT()function, the use ofcountas a table name in the following statement causes an error:mysql>
CREATE TABLE count (i INT);ERROR 1064 (42000): You have an error in your SQL syntaxThe table name should be quoted:
mysql>
CREATE TABLE `count` (i INT);Query OK, 0 rows affected (0.00 sec)The
IGNORE_SPACESQL mode applies to built-in functions, not to user-defined functions or stored functions. It is always permissible to have spaces after a UDF or stored function name, regardless of whetherIGNORE_SPACEis enabled.For further discussion of
IGNORE_SPACE, see Section 10.2.4, “Function Name Parsing and Resolution”.Prevent the
GRANTstatement from automatically creating new user accounts if it would otherwise do so, unless authentication information is specified. The statement must specify a nonempty password usingIDENTIFIED BYor an authentication plugin usingIDENTIFIED WITH.It is preferable to create MySQL accounts with
CREATE USERrather thanGRANT. As of MySQL 5.7.6,NO_AUTO_CREATE_USERis deprecated. As of 5.7.7 the default SQL mode includesNO_AUTO_CREATE_USERand assignments tosql_modethat change theNO_AUTO_CREATE_USERmode state produce a warning, except assignments that setsql_modetoDEFAULT.NO_AUTO_CREATE_USERwill be removed in a future MySQL release, at which point its effect will be enabled at all times (GRANTwill not create accounts).NO_AUTO_VALUE_ON_ZEROaffects handling ofAUTO_INCREMENTcolumns. Normally, you generate the next sequence number for the column by inserting eitherNULLor0into it.NO_AUTO_VALUE_ON_ZEROsuppresses this behavior for0so that onlyNULLgenerates the next sequence number.This mode can be useful if
0has been stored in a table'sAUTO_INCREMENTcolumn. (Storing0is not a recommended practice, by the way.) For example, if you dump the table with mysqldump and then reload it, MySQL normally generates new sequence numbers when it encounters the0values, resulting in a table with contents different from the one that was dumped. EnablingNO_AUTO_VALUE_ON_ZERObefore reloading the dump file solves this problem. mysqldump now automatically includes in its output a statement that enablesNO_AUTO_VALUE_ON_ZERO, to avoid this problem.Disable the use of the backslash character (“
\”) as an escape character within strings. With this mode enabled, backslash becomes an ordinary character like any other.When creating a table, ignore all
INDEX DIRECTORYandDATA DIRECTORYdirectives. This option is useful on slave replication servers.Control automatic substitution of the default storage engine when a statement such as
CREATE TABLEorALTER TABLEspecifies a storage engine that is disabled or not compiled in.The default SQL mode includes
NO_ENGINE_SUBSTITUTION.Because storage engines can be pluggable at runtime, unavailable engines are treated the same way:
With
NO_ENGINE_SUBSTITUTIONdisabled, forCREATE TABLEthe default engine is used and a warning occurs if the desired engine is unavailable. ForALTER TABLE, a warning occurs and the table is not altered.With
NO_ENGINE_SUBSTITUTIONenabled, an error occurs and the table is not created or altered if the desired engine is unavailable.Do not print MySQL-specific column options in the output of
SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.Do not print MySQL-specific index options in the output of
SHOW CREATE TABLE. This mode is used by mysqldump in portability mode.Do not print MySQL-specific table options (such as
ENGINE) in the output ofSHOW CREATE TABLE. This mode is used by mysqldump in portability mode.Subtraction between integer values, where one is of type
UNSIGNED, produces an unsigned result by default. If the result would otherwise have been negative, an error results:mysql>
SET sql_mode = '';Query OK, 0 rows affected (0.00 sec) mysql>SELECT CAST(0 AS UNSIGNED) - 1;ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '(cast(0 as unsigned) - 1)'If the
NO_UNSIGNED_SUBTRACTIONSQL mode is enabled, the result is negative:mysql>
SET sql_mode = 'NO_UNSIGNED_SUBTRACTION';mysql>SELECT CAST(0 AS UNSIGNED) - 1;+-------------------------+ | CAST(0 AS UNSIGNED) - 1 | +-------------------------+ | -1 | +-------------------------+If the result of such an operation is used to update an
UNSIGNEDinteger column, the result is clipped to the maximum value for the column type, or clipped to 0 ifNO_UNSIGNED_SUBTRACTIONis enabled. If strict SQL mode is enabled, an error occurs and the column remains unchanged.When
NO_UNSIGNED_SUBTRACTIONis enabled, the subtraction result is signed, even if any operand is unsigned. For example, compare the type of columnc2in tablet1with that of columnc2in tablet2:mysql>
SET sql_mode='';mysql>CREATE TABLE test (c1 BIGINT UNSIGNED NOT NULL);mysql>CREATE TABLE t1 SELECT c1 - 1 AS c2 FROM test;mysql>DESCRIBE t1;+-------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------------------+------+-----+---------+-------+ | c2 | bigint(21) unsigned | NO | | 0 | | +-------+---------------------+------+-----+---------+-------+ mysql>SET sql_mode='NO_UNSIGNED_SUBTRACTION';mysql>CREATE TABLE t2 SELECT c1 - 1 AS c2 FROM test;mysql>DESCRIBE t2;+-------+------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+------------+------+-----+---------+-------+ | c2 | bigint(21) | NO | | 0 | | +-------+------------+------+-----+---------+-------+This means that
BIGINT UNSIGNEDis not 100% usable in all contexts. See Section 13.10, “Cast Functions and Operators”.The
NO_ZERO_DATEmode affects whether the server permits'0000-00-00'as a valid date. Its effect also depends on whether strict SQL mode is enabled.If this mode is not enabled,
'0000-00-00'is permitted and inserts produce no warning.If this mode is enabled,
'0000-00-00'is permitted and inserts produce a warning.If this mode and strict mode are enabled,
'0000-00-00'is not permitted and inserts produce an error, unlessIGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE,'0000-00-00'is permitted and inserts produce a warning.
As of MySQL 5.7.4,
NO_ZERO_DATEis deprecated. In MySQL 5.7.4 through 5.7.7,NO_ZERO_DATEdoes nothing when named explicitly. Instead, its effect is included in the effects of strict SQL mode. In MySQL 5.7.8 and later,NO_ZERO_DATEdoes have an effect when named explicitly and is not part of strict mode, as before MySQL 5.7.4. However, it should be used in conjunction with strict mode and is enabled by default. A warning occurs ifNO_ZERO_DATEis enabled without also enabling strict mode or vice versa. For additional discussion, see SQL Mode Changes in MySQL 5.7.Because
NO_ZERO_DATEis deprecated, it will be removed in a future MySQL release as a separate mode name and its effect included in the effects of strict SQL mode.The
NO_ZERO_IN_DATEmode affects whether the server permits dates in which the year part is nonzero but the month or day part is 0. (This mode affects dates such as'2010-00-01'or'2010-01-00', but not'0000-00-00'. To control whether the server permits'0000-00-00', use theNO_ZERO_DATEmode.) The effect ofNO_ZERO_IN_DATEalso depends on whether strict SQL mode is enabled.If this mode is not enabled, dates with zero parts are permitted and inserts produce no warning.
If this mode is enabled, dates with zero parts are inserted as
'0000-00-00'and produce a warning.If this mode and strict mode are enabled, dates with zero parts are not permitted and inserts produce an error, unless
IGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE, dates with zero parts are inserted as'0000-00-00'and produce a warning.
As of MySQL 5.7.4,
NO_ZERO_IN_DATEis deprecated. In MySQL 5.7.4 through 5.7.7,NO_ZERO_IN_DATEdoes nothing when named explicitly. Instead, its effect is included in the effects of strict SQL mode. In MySQL 5.7.8 and later,NO_ZERO_IN_DATEdoes have an effect when named explicitly and is not part of strict mode, as before MySQL 5.7.4. However, it should be used in conjunction with strict mode and is enabled by default. A warning occurs ifNO_ZERO_IN_DATEis enabled without also enabling strict mode or vice versa. For additional discussion, see SQL Mode Changes in MySQL 5.7.Because
NO_ZERO_IN_DATEis deprecated, it will be removed in a future MySQL release as a separate mode name and its effect included in the effects of strict SQL mode.Reject queries for which the select list,
HAVINGcondition, orORDER BYlist refer to nonaggregated columns that are neither named in theGROUP BYclause nor are functionally dependent on (uniquely determined by)GROUP BYcolumns.As of MySQL 5.7.5, the default SQL mode includes
ONLY_FULL_GROUP_BY. (Before 5.7.5, MySQL does not detect functional dependency andONLY_FULL_GROUP_BYis not enabled by default. For a description of pre-5.7.5 behavior, see the MySQL 5.6 Reference Manual.)A MySQL extension to standard SQL permits references in the
HAVINGclause to aliased expressions in the select list. Before MySQL 5.7.5, enablingONLY_FULL_GROUP_BYdisables this extension, thus requiring theHAVINGclause to be written using unaliased expressions. As of MySQL 5.7.5, this restriction is lifted so that theHAVINGclause can refer to aliases regardless of whetherONLY_FULL_GROUP_BYis enabled.For additional discussion and examples, see Section 13.20.3, “MySQL Handling of GROUP BY”.
By default, trailing spaces are trimmed from
CHARcolumn values on retrieval. IfPAD_CHAR_TO_FULL_LENGTHis enabled, trimming does not occur and retrievedCHARvalues are padded to their full length. This mode does not apply toVARCHARcolumns, for which trailing spaces are retained on retrieval.mysql>
CREATE TABLE t1 (c1 CHAR(10));Query OK, 0 rows affected (0.37 sec) mysql>INSERT INTO t1 (c1) VALUES('xy');Query OK, 1 row affected (0.01 sec) mysql>SET sql_mode = '';Query OK, 0 rows affected (0.00 sec) mysql>SELECT c1, CHAR_LENGTH(c1) FROM t1;+------+-----------------+ | c1 | CHAR_LENGTH(c1) | +------+-----------------+ | xy | 2 | +------+-----------------+ 1 row in set (0.00 sec) mysql>SET sql_mode = 'PAD_CHAR_TO_FULL_LENGTH';Query OK, 0 rows affected (0.00 sec) mysql>SELECT c1, CHAR_LENGTH(c1) FROM t1;+------------+-----------------+ | c1 | CHAR_LENGTH(c1) | +------------+-----------------+ | xy | 10 | +------------+-----------------+ 1 row in set (0.00 sec)Treat
||as a string concatenation operator (same asCONCAT()) rather than as a synonym forOR.Treat
REALas a synonym forFLOAT. By default, MySQL treatsREALas a synonym forDOUBLE.Enable strict SQL mode for all storage engines. Invalid data values are rejected. For details, see Strict SQL Mode.
From MySQL 5.7.4 through 5.7.7,
STRICT_ALL_TABLESincludes the effect of theERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATEmodes. For additional discussion, see SQL Mode Changes in MySQL 5.7.Enable strict SQL mode for transactional storage engines, and when possible for nontransactional storage engines. For details, see Strict SQL Mode.
From MySQL 5.7.4 through 5.7.7,
STRICT_TRANS_TABLESincludes the effect of theERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATEmodes. For additional discussion, see SQL Mode Changes in MySQL 5.7.
The following special modes are provided as shorthand for combinations of mode values from the preceding list.
Equivalent to
REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE, and (as of MySQL 5.7.5)ONLY_FULL_GROUP_BY.ANSImode also causes the server to return an error for queries where a set functionSwith an outer referenceS(outer_ref)SELECT * FROM t1 WHERE t1.a IN (SELECT MAX(t1.b) FROM t2 WHERE ...);
Here,
MAX(t1.b)cannot aggregated in the outer query because it appears in theWHEREclause of that query. Standard SQL requires an error in this situation. IfANSImode is not enabled, the server treatsS(outer_ref)S(const)Equivalent to
PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS.Equivalent to
PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS,NO_AUTO_CREATE_USER.Equivalent to
PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS.Equivalent to
MYSQL323,HIGH_NOT_PRECEDENCE. This meansHIGH_NOT_PRECEDENCEplus someSHOW CREATE TABLEbehaviors specific toMYSQL323:TIMESTAMPcolumn display does not includeDEFAULTorON UPDATEattributes that were introduced in MySQL 4.1.String column display does not include character set and collation attributes that were introduced in MySQL 4.1. For
CHARandVARCHARcolumns, if the collation is binary,BINARYis appended to the column type.The
ENGINE=table option displays asengine_nameTYPE=.engine+nameFor
MEMORYtables, the storage engine is displayed asHEAP.
Equivalent to
MYSQL40,HIGH_NOT_PRECEDENCE. This meansHIGH_NOT_PRECEDENCEplus some behaviors specific toMYSQL40. These are the same as forMYSQL323, except thatSHOW CREATE TABLEdoes not displayHEAPas the storage engine forMEMORYtables.Equivalent to
PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS,NO_AUTO_CREATE_USER.Equivalent to
PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,NO_KEY_OPTIONS,NO_TABLE_OPTIONS,NO_FIELD_OPTIONS.Before MySQL 5.7.4, and in MySQL 5.7.8 and later,
TRADITIONALis equivalent toSTRICT_TRANS_TABLES,STRICT_ALL_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER, andNO_ENGINE_SUBSTITUTION.From MySQL 5.7.4 though 5.7.7,
TRADITIONALis equivalent toSTRICT_TRANS_TABLES,STRICT_ALL_TABLES,NO_AUTO_CREATE_USER, andNO_ENGINE_SUBSTITUTION. TheNO_ZERO_IN_DATE,NO_ZERO_DATE, andERROR_FOR_DIVISION_BY_ZEROmodes are not named because in those versions their effects are included in the effects of strict SQL mode (STRICT_ALL_TABLESorSTRICT_TRANS_TABLES). Thus, the effects ofTRADITIONALare the same in all MySQL 5.7 versions (and the same as in MySQL 5.6). For additional discussion, see SQL Mode Changes in MySQL 5.7.
Strict mode controls how MySQL handles invalid or missing values
in data-change statements such as
INSERT or
UPDATE. A value can be invalid
for several reasons. For example, it might have the wrong data
type for the column, or it might be out of range. A value is
missing when a new row to be inserted does not contain a value
for a non-NULL column that has no explicit
DEFAULT clause in its definition. (For a
NULL column, NULL is
inserted if the value is missing.) Strict mode also affects DDL
statements such as CREATE TABLE.
If strict mode is not in effect, MySQL inserts adjusted values
for invalid or missing values and produces warnings (see
Section 14.7.5.40, “SHOW WARNINGS Syntax”). In strict mode, you can
produce this behavior by using
INSERT IGNORE
or UPDATE
IGNORE.
For statements such as SELECT
that do not change data, invalid values generate a warning in
strict mode, not an error.
Strict mode produces an error for attempts to create a key that exceeds the maximum key length. When strict mode is not enabled, this results in a warning and truncation of the key to the maximum key length.
Strict mode does not affect whether foreign key constraints are
checked. foreign_key_checks can
be used for that. (See
Section 6.1.4, “Server System Variables”.)
Strict SQL mode is in effect if either
STRICT_ALL_TABLES or
STRICT_TRANS_TABLES is
enabled, although the effects of these modes differ somewhat:
For transactional tables, an error occurs for invalid or missing values in a data-change statement when either
STRICT_ALL_TABLESorSTRICT_TRANS_TABLESis enabled. The statement is aborted and rolled back.For nontransactional tables, the behavior is the same for either mode if the bad value occurs in the first row to be inserted or updated: The statement is aborted and the table remains unchanged. If the statement inserts or modifies multiple rows and the bad value occurs in the second or later row, the result depends on which strict mode is enabled:
For
STRICT_ALL_TABLES, MySQL returns an error and ignores the rest of the rows. However, because the earlier rows have been inserted or updated, the result is a partial update. To avoid this, use single-row statements, which can be aborted without changing the table.For
STRICT_TRANS_TABLES, MySQL converts an invalid value to the closest valid value for the column and inserts the adjusted value. If a value is missing, MySQL inserts the implicit default value for the column data type. In either case, MySQL generates a warning rather than an error and continues processing the statement. Implicit defaults are described in Section 12.7, “Data Type Default Values”.
Strict mode affects handling of division by zero, zero dates, and zeros in dates as follows:
Strict mode affects handling of division by zero, which includes
MOD(:N,0)For data-change operations (
INSERT,UPDATE):If strict mode is not enabled, division by zero inserts
NULLand produces no warning.If strict mode is enabled, division by zero produces an error, unless
IGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE, division by zero insertsNULLand produces a warning.
For
SELECT, division by zero returnsNULL. Enabling strict mode causes a warning to be produced as well.Strict mode affects whether the server permits
'0000-00-00'as a valid date:If strict mode is not enabled,
'0000-00-00'is permitted and inserts produce no warning.If strict mode is enabled,
'0000-00-00'is not permitted and inserts produce an error, unlessIGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE,'0000-00-00'is permitted and inserts produce a warning.
Strict mode affects whether the server permits dates in which the year part is nonzero but the month or day part is 0 (dates such as
'2010-00-01'or'2010-01-00'):If strict mode is not enabled, dates with zero parts are permitted and inserts produce no warning.
If strict mode is enabled, dates with zero parts are not permitted and inserts produce an error, unless
IGNOREis given as well. ForINSERT IGNOREandUPDATE IGNORE, dates with zero parts are inserted as'0000-00-00'(which is considered valid withIGNORE) and produce a warning.
For more information about strict mode with respect to
IGNORE, see
Comparison of the IGNORE Keyword and Strict SQL Mode.
Before MySQL 5.7.4, and in MySQL 5.7.8 and later, strict mode
affects handling of division by zero, zero dates, and zeros in
dates in conjunction with the
ERROR_FOR_DIVISION_BY_ZERO,
NO_ZERO_DATE, and
NO_ZERO_IN_DATE modes. From
MySQL 5.7.4 though 5.7.7, the
ERROR_FOR_DIVISION_BY_ZERO,
NO_ZERO_DATE, and
NO_ZERO_IN_DATE modes do
nothing when named explicitly and their effects are included in
the effects of strict mode. For additional discussion, see
SQL Mode Changes in MySQL 5.7.
This section compares the effect on statement execution of the
IGNORE keyword (which downgrades errors to
warnings) and strict SQL mode (which upgrades warnings to
errors). It describes which statements they affect, and which
errors they apply to.
The following table presents a summary comparison of statement
behavior when the default is to produce an error versus a
warning. An example of when the default is to produce an error
is inserting a NULL into a NOT
NULL column. An example of when the default is to
produce a warning is inserting a value of the wrong data type
into a column (such as inserting the string
'abc' into an integer column).
| Operational Mode | When Statement Default is Error | When Statement Default is Warning |
|---|---|---|
Without IGNORE or strict SQL mode | Error | Warning |
With IGNORE | Warning | Warning (same as without IGNORE or strict SQL mode) |
| With strict SQL mode | Error (same as without IGNORE or strict SQL mode) | Error |
With IGNORE and strict SQL mode | Warning | Warning |
One conclusion to draw from the table is that when the
IGNORE keyword and strict SQL mode are both
in effect, IGNORE takes precedence. This
means that, although IGNORE and strict SQL
mode can be considered to have opposite effects on error
handling, they do not cancel when used together.
The Effect of IGNORE on Statement Execution
Several statements in MySQL support an optional
IGNORE keyword. This keyword causes the
server to downgrade certain types of errors and generate
warnings instead. For a multiple-row statement,
IGNORE causes the statement to skip to the
next row instead of aborting.
For example, if the table t has a primary key
column i, attempting to insert the same value
of i into multiple rows normally produces a
duplicate-key error:
mysql> INSERT INTO t (i) VALUES(1),(1);
ERROR 1062 (23000): Duplicate entry '1' for key 'PRIMARY'
With IGNORE, the row containing the duplicate
key still is not inserted, but a warning occurs instead of an
error:
mysql>INSERT IGNORE INTO t (i) VALUES(1),(1);Query OK, 1 row affected, 1 warning (0.01 sec) Records: 2 Duplicates: 1 Warnings: 1 mysql>SHOW WARNINGS;+---------+------+---------------------------------------+ | Level | Code | Message | +---------+------+---------------------------------------+ | Warning | 1062 | Duplicate entry '1' for key 'PRIMARY' | +---------+------+---------------------------------------+ 1 row in set (0.00 sec)
These statements support the IGNORE keyword:
CREATE TABLE ... SELECT:IGNOREdoes not apply to theCREATE TABLEorSELECTparts of the statement but to inserts into the table of rows produced by theSELECT. Rows that duplicate an existing row on a unique key value are discarded.DELETE:IGNOREcauses MySQL to ignore errors during the process of deleting rows.INSERT: WithIGNORE, rows that duplicate an existing row on a unique key value are discarded. Rows set to values that would cause data conversion errors are set to the closest valid values instead.For partitioned tables where no partition matching a given value is found,
IGNOREcauses the insert operation to fail silently for rows containing the unmatched value.LOAD DATA,LOAD XML: WithIGNORE, rows that duplicate an existing row on a unique key value are discarded.UPDATE: WithIGNORE, rows for which duplicate-key conflicts occur on a unique key value are not updated. Rows updated to values that would cause data conversion errors are updated to the closest valid values instead.
The IGNORE keyword applies to the following
errors:
ER_BAD_NULL_ERRORER_DUP_ENTRYER_DUP_ENTRY_WITH_KEY_NAMEER_DUP_KEYER_NO_PARTITION_FOR_GIVEN_VALUEER_NO_PARTITION_FOR_GIVEN_VALUE_SILENTER_NO_REFERENCED_ROW_2ER_ROW_DOES_NOT_MATCH_GIVEN_PARTITION_SETER_ROW_IS_REFERENCED_2ER_SUBQUERY_NO_1_ROWER_VIEW_CHECK_FAILED
The Effect of Strict SQL Mode on Statement Execution
The MySQL server can operate in different SQL modes, and can
apply these modes differently for different clients, depending
on the value of the sql_mode
system variable. In “strict” SQL mode, the server
upgrades certain warnings to errors.
For example, in non-strict SQL mode, inserting the string
'abc' into an integer column results in
conversion of the value to 0 and a warning:
mysql>SET sql_mode = '';Query OK, 0 rows affected (0.00 sec) mysql>INSERT INTO t (i) VALUES('abc');Query OK, 1 row affected, 1 warning (0.01 sec) mysql>SHOW WARNINGS;+---------+------+--------------------------------------------------------+ | Level | Code | Message | +---------+------+--------------------------------------------------------+ | Warning | 1366 | Incorrect integer value: 'abc' for column 'i' at row 1 | +---------+------+--------------------------------------------------------+ 1 row in set (0.00 sec)
In strict SQL mode, the invalid value is rejected with an error:
mysql>SET sql_mode = 'STRICT_ALL_TABLES';Query OK, 0 rows affected (0.00 sec) mysql>INSERT INTO t (i) VALUES('abc');ERROR 1366 (HY000): Incorrect integer value: 'abc' for column 'i' at row 1
For more information about possible settings of the
sql_mode system variable, see
Section 6.1.7, “Server SQL Modes”.
Strict SQL mode applies to the following statements under conditions for which some value might be out of range or an invalid row is inserted into or deleted from a table:
Within stored programs, individual statements of the types just listed execute in strict SQL mode if the program was defined while strict mode was in effect.
Strict SQL mode applies to the following errors, represent a
class of errors in which an input value is either invalid or
missing. A value is invalid if it has the wrong data type for
the column or might be out of range. A value is missing if a new
row to be inserted does not contain a value for a NOT
NULL column that has no explicit
DEFAULT clause in its definition.
ER_BAD_NULL_ERRORER_CUT_VALUE_GROUP_CONCATER_DATA_TOO_LONGER_DATETIME_FUNCTION_OVERFLOWER_DIVISION_BY_ZEROER_INVALID_ARGUMENT_FOR_LOGARITHMER_NO_DEFAULT_FOR_FIELDER_NO_DEFAULT_FOR_VIEW_FIELDER_TOO_LONG_KEYER_TRUNCATED_WRONG_VALUEER_TRUNCATED_WRONG_VALUE_FOR_FIELDER_WARN_DATA_OUT_OF_RANGEER_WARN_NULL_TO_NOTNULLER_WARN_TOO_FEW_RECORDSER_WRONG_ARGUMENTSER_WRONG_VALUE_FOR_TYPEWARN_DATA_TRUNCATED
In MySQL 5.7.5, the
ONLY_FULL_GROUP_BY SQL mode is
enabled by default because GROUP BY
processing has become more sophisticated to include detection of
functional dependencies. However, if you find that having
ONLY_FULL_GROUP_BY enabled
causes queries for existing applications to be rejected, either
of these actions should restore operation:
If it is possible to modify an offending query, do so, either so that nonaggregated columns are functionally dependent on
GROUP BYcolumns, or by referring to nonaggregated columns usingANY_VALUE().If it is not possible to modify an offending query (for example, if it is generated by a third-party application), set the
sql_modesystem variable at server startup to not enableONLY_FULL_GROUP_BY.
As of MySQL 5.7.4, the
ERROR_FOR_DIVISION_BY_ZERO,
NO_ZERO_DATE, and
NO_ZERO_IN_DATE SQL modes are
deprecated. From MySQL 5.7.4 though 5.7.7, these modes do
nothing when named explicitly. Instead, their effects are
included in the effects of strict SQL mode
(STRICT_ALL_TABLES or
STRICT_TRANS_TABLES). In other
words, strict mode means the same thing in those versions as the
pre-5.7.4 meaning of strict mode plus
ERROR_FOR_DIVISION_BY_ZERO,
NO_ZERO_DATE, and
NO_ZERO_IN_DATE.
The MySQL 5.7.4 change to make strict mode more strict by
including
ERROR_FOR_DIVISION_BY_ZERO,
NO_ZERO_DATE, and
NO_ZERO_IN_DATE caused some
problems. For example, in MySQL 5.6 with strict mode but not
NO_ZERO_DATE enabled,
TIMESTAMP columns can be defined
with DEFAULT '0000-00-00 00:00:00'. In MySQL
5.7.4 with the same mode settings, strict mode includes the
effect of NO_ZERO_DATE and
TIMESTAMP columns cannot be
defined with DEFAULT '0000-00-00 00:00:00'.
This causes replication of CREATE
TABLE statements from 5.6 to 5.7.4 to fail if they
contain such TIMESTAMP columns.
The long term plan is still to have the three affected modes be included in strict SQL mode and to remove them as explicit modes in a future MySQL release. But to restore compatibility in MySQL 5.7 with MySQL 5.6 strict mode and to provide additional time for affected applications to be modified, the following changes were made in MySQL 5.7.8:
ERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATEhave an effect when named explicitly. This reverts a change made in MySQL 5.7.4.ERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATEare not part of strict SQL mode. This reverts a change made in MySQL 5.7.4.ERROR_FOR_DIVISION_BY_ZERO,NO_ZERO_DATE, andNO_ZERO_IN_DATEare included in the defaultsql_modevalue, which as a result includes these modes:ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER, andNO_ENGINE_SUBSTITUTION.
With the preceding changes, stricter data checking is still enabled by default, but the individual modes can be disabled in environments where it is currently desirable or necessary to do so.
Although in MySQL 5.7.8 and later
ERROR_FOR_DIVISION_BY_ZERO,
NO_ZERO_DATE, and
NO_ZERO_IN_DATE can be used
separately from strict mode, it is intended that they be used
together. As a reminder, a warning occurs if they are enabled
without also enabling strict mode or vice versa.
The following discussion applies only for MySQL versions 5.7.4 through 5.7.7. For upgrades from a version older than MySQL 5.7.4, we recommend upgrading to MySQL 5.7.8 or later, which renders this discussion unnecessary.
The remainder of this section describes the SQL mode settings to
use in MySQL 5.7.4 through 5.7.7 to achieve the same statement
execution as before 5.7.4, including the cases for
INSERT and
UPDATE in which
IGNORE is given. It also provides guidelines
for determining whether applications need modification to behave
the same before and after the SQL mode changes.
The following table shows how to control handling of division by zero for versions other than MySQL 5.7.4 through 5.7.7 and for MySQL 5.7.4 through 5.7.7.
| Desired Behavior | MySQL 5.7.x Versions Except 5.7.4 Through 5.7.7 | MySQL 5.7.4 Through 5.7.7 |
|---|---|---|
insert NULL, produce no warning | ERROR_FOR_DIVISION_BY_ZERO not enabled | strict mode not enabled |
insert NULL, produce warning | ERROR_FOR_DIVISION_BY_ZERO, or
ERROR_FOR_DIVISION_BY_ZERO + strict
mode + IGNORE | strict mode + IGNORE |
| error | ERROR_FOR_DIVISION_BY_ZERO + strict mode | strict mode |
The following table shows how to control whether the server
permits '0000-00-00' as a valid date for
versions other than MySQL 5.7.4 through 5.7.7 and for MySQL
5.7.4 through 5.7.7.
| Desired Behavior | MySQL 5.7.x Versions Except 5.7.4 Through 5.7.7 | MySQL 5.7.4 Through 5.7.7 |
|---|---|---|
insert '0000-00-00', produce no warning | NO_ZERO_DATE not enabled | strict mode not enabled |
insert '0000-00-00', produce warning | NO_ZERO_DATE, or NO_ZERO_DATE +
strict mode + IGNORE | strict mode + IGNORE |
| error | NO_ZERO_DATE + strict mode | strict mode |
The following table shows how to control whether the server permits dates with zero parts for versions other than MySQL 5.7.4 through 5.7.7 and for MySQL 5.7.4 through 5.7.7.
| Desired Behavior | MySQL 5.7.x Versions Except 5.7.4 Through 5.7.7 | MySQL 5.7.4 Through 5.7.7 |
|---|---|---|
| insert date, produce no warning | NO_ZERO_IN_DATE not enabled | strict mode not enabled |
insert '0000-00-00', produce warning | NO_ZERO_IN_DATE, or
NO_ZERO_IN_DATE + strict mode +
IGNORE | strict mode + IGNORE |
| error | NO_ZERO_IN_DATE + strict mode | strict mode |
The following discussion describes the conditions under which a
given statement produces the same or different result under the
SQL mode changes in MySQL 5.7.4 through 5.7.7. It considers only
strict mode (STRICT_ALL_TABLES
or STRICT_TRANS_TABLES) and
the three deprecated modes
(ERROR_FOR_DIVISION_BY_ZERO,
NO_ZERO_DATE, and
NO_ZERO_IN_DATE). Other SQL
modes such as ANSI_QUOTES or
ONLY_FULL_GROUP_BY are assumed
to be held constant before and after an upgrade.
This discussion also describes how to prepare for an upgrade to 5.7.4 through 5.7.7 from a version older than 5.7.4. Any modifications should be made before upgrading.
There is no change in behavior between MySQL 5.6 and 5.7 for the following SQL mode settings. A statement that executes under one of these settings needs no modification to produce the same result in 5.6 and 5.7:
Strict mode and the three deprecated modes are all not enabled.
Strict mode and the three deprecated modes are all enabled.
A change from warnings in MySQL 5.6 to no warnings in MySQL 5.7 occurs for the following SQL mode settings. The result of statement execution is the same in 5.6 and 5.7, so statements need no modification unless warnings are considered significant:
Strict mode is not enabled, but either of the deprecated
ERROR_FOR_DIVISION_BY_ZEROandNO_ZERO_DATEmodes are enabled.
A behavior change occurs under the following SQL mode settings. A statement that executes under one of these settings must be modified to produce the same result in 5.6 and 5.7:
Strict mode is not enabled,
NO_ZERO_IN_DATEis enabled. For this mode setting, expect these differences in statement execution:In 5.6, the server inserts dates with zero parts as
'0000-00-00'and produces a warning.In 5.7, the server inserts dates with zero parts as is and produces no warning.
Strict mode is enabled, with some but not all of the three deprecated modes enabled. For this mode setting, expect these differences in statement execution:
Statements that would be affected by enabling the not-enabled deprecated modes produce errors in 5.7 but not in 5.6. Suppose that strict mode,
NO_ZERO_DATE, andNO_ZERO_IN_DATEare enabled, and a data-change statement performs division by zero:In 5.6, the statement inserts
NULLand produces no warning. EnablingERROR_FOR_DIVISION_BY_ZEROwould cause an error instead.In 5.7, an error occurs because strict mode implicitly includes the effect of
ERROR_FOR_DIVISION_BY_ZERO. EnablingERROR_FOR_DIVISION_BY_ZEROexplicitly would not change that.
To prepare for an upgrade to MySQL 5.7.4 through 5.7.7, the main principle is to make sure that your applications will operate the same way in MySQL 5.6 and 5.7. For example, you can adopt either of these approaches to application compatibility:
Modify the application to set the SQL mode on a version-specific basis. If we assume that an application will not be used with development versions of MySQL 5.7 prior to 5.7.4, it is possible to set the
sql_modevalue for the application based on the current server version as follows:SET sql_mode = IF(LEFT(VERSION(),3)<'5.7',
5.6 mode,5.7 mode);The tables shown earlier in this section serve as a guide to the appropriate equivalent modes for MySQL 5.6 and 5.7.
Modify the application to execute under an SQL mode for which statements produce the same result in MySQL 5.6 and 5.7.
TipTRADITIONALSQL mode in MySQL 5.6 includes strict mode and the three deprecated modes. If you write applications to operate inTRADITIONALmode in MySQL 5.6, there is no change to make for MySQL 5.7.
When assessing SQL mode compatibility between MySQL 5.6 and 5.7, consider particularly these statement execution contexts:
Replication. You will encounter replication incompatibility related to the SQL mode changes under the following conditions:
MySQL 5.6 master and 5.7 slave
Statement-based replication
An SQL mode setting for which statements produce different results in MySQL 5.6 and 5.7, as described earlier
To handle this incompatibility, use one of these workarounds:
Use row-based replication
Use
IGNOREUse an SQL mode for which statements do not produce different results in MySQL 5.6 and 5.7
Stored programs (stored procedures and functions, triggers, and events). Each stored program executes using the SQL mode in effect at the time it was created. To identify stored programs that may be affected by differences between MySQL 5.6 and 5.7 in SQL mode handling, use these queries:
SELECT ROUTINE_SCHEMA, ROUTINE_NAME, ROUTINE_TYPE, SQL_MODE FROM INFORMATION_SCHEMA.ROUTINES WHERE SQL_MODE LIKE '%STRICT%' OR SQL_MODE LIKE '%DIVISION%' OR SQL_MODE LIKE '%NO_ZERO%'; SELECT TRIGGER_SCHEMA, TRIGGER_NAME, SQL_MODE FROM INFORMATION_SCHEMA.TRIGGERS WHERE SQL_MODE LIKE '%STRICT%' OR SQL_MODE LIKE '%DIVISION%' OR SQL_MODE LIKE '%NO_ZERO%'; SELECT EVENT_SCHEMA, EVENT_NAME, SQL_MODE FROM INFORMATION_SCHEMA.EVENTS WHERE SQL_MODE LIKE '%STRICT%' OR SQL_MODE LIKE '%DIVISION%' OR SQL_MODE LIKE '%NO_ZERO%';
Support for IPv6 in MySQL includes these capabilities:
MySQL Server can accept TCP/IP connections from clients connecting over IPv6. For example, this command connects over IPv6 to the MySQL server on the local host:
shell>
mysql -h ::1To use this capability, two things must be true:
Your system must be configured to support IPv6. See Section 6.1.8.1, “Verifying System Support for IPv6”.
The default MySQL server configuration permits IPv6 connections in addition to IPv4 connections. To change the default configuration, start the server with an appropriate
--bind-addressoption. See Section 6.1.4, “Server System Variables”.
MySQL account names permit IPv6 addresses to enable DBAs to specify privileges for clients that connect to the server over IPv6. See Section 7.2.3, “Specifying Account Names”. IPv6 addresses can be specified in account names in statements such as
CREATE USER,GRANT, andREVOKE. For example:mysql>
CREATE USER 'bill'@'::1' IDENTIFIED BY 'secret';mysql>GRANT SELECT ON mydb.* TO 'bill'@'::1';IPv6 functions enable conversion between string and internal format IPv6 address formats, and checking whether values represent valid IPv6 addresses. For example,
INET6_ATON()andINET6_NTOA()are similar toINET_ATON()andINET_NTOA(), but handle IPv6 addresses in addition to IPv4 addresses. See Section 13.19, “Miscellaneous Functions”.
The following sections describe how to set up MySQL so that clients can connect to the server over IPv6.
Before MySQL Server can accept IPv6 connections, the operating system on your server host must support IPv6. As a simple test to determine whether that is true, try this command:
shell> ping6 ::1
16 bytes from ::1, icmp_seq=0 hlim=64 time=0.171 ms
16 bytes from ::1, icmp_seq=1 hlim=64 time=0.077 ms
...
To produce a description of your system's network interfaces, invoke ifconfig -a and look for IPv6 addresses in the output.
If your host does not support IPv6, consult your system documentation for instructions on enabling it. It might be that you need only reconfigure an existing network interface to add an IPv6 address. Or a more extensive change might be needed, such as rebuilding the kernel with IPv6 options enabled.
These links may be helpful in setting up IPv6 on various platforms:
The MySQL server listens on a single network socket for TCP/IP
connections. This socket is bound to a single address, but it is
possible for an address to map onto multiple network interfaces.
To specify an address, use the
--bind-address=
option at server startup, where addraddr
is an IPv4 or IPv6 address or a host name. (IPv6 addresses are
not supported before MySQL 5.5.3.) If
addr is a host name, the server
resolves the name to an IP address and binds to that address.
The server treats different types of addresses as follows:
If the address is
*, the server accepts TCP/IP connections on all server host IPv6 and IPv4 interfaces if the server host supports IPv6, or accepts TCP/IP connections on all IPv4 addresses otherwise. Use this address to permit both IPv4 and IPv6 connections on all server interfaces. This value is the default.If the address is
0.0.0.0, the server accepts TCP/IP connections on all server host IPv4 interfaces.If the address is
::, the server accepts TCP/IP connections on all server host IPv4 and IPv6 interfaces. Use this address to permit both IPv4 and IPv6 connections on all server interfaces.If the address is an IPv4-mapped address, the server accepts TCP/IP connections for that address, in either IPv4 or IPv6 format. For example, if the server is bound to
::ffff:127.0.0.1, clients can connect using--host=127.0.0.1or--host=::ffff:127.0.0.1.If the address is a “regular” IPv4 or IPv6 address (such as
127.0.0.1or::1), the server accepts TCP/IP connections only for that IPv4 or IPv6 address.
If you intend to bind the server to a specific address, be sure
that the mysql.user grant table contains an
account with administrative privileges that you can use to
connect to that address. Otherwise, you will not be able to shut
down the server. For example, if you bind the server to
*, you can connect to it using all existing
accounts. But if you bind the server to ::1,
it accepts connections only on that address. In that case, first
make sure that the 'root'@'::1' account is
present in the mysql.user table so you can
still connect to the server to shut it down.
The following procedure shows how to configure MySQL to permit
IPv6 connections by clients that connect to the local server
using the ::1 local host address. The
instructions given here assume that your system supports IPv6.
Start the MySQL server with an appropriate
--bind-addressoption to permit it to accept IPv6 connections. For example, put the following lines in your server option file and restart the server:[mysqld] bind-address = *
Alternatively, you can bind the server to
::1, but that makes the server more restrictive for TCP/IP connections. It accepts only IPv6 connections for that single address and rejects IPv4 connections. For more information, see Section 6.1.8.2, “Configuring the MySQL Server to Permit IPv6 Connections”.As an administrator, connect to the server and create an account for a local user who will connect from the
::1local IPv6 host address:mysql>
CREATE USER 'ipv6user'@'::1' IDENTIFIED BY 'ipv6pass';For the permitted syntax of IPv6 addresses in account names, see Section 7.2.3, “Specifying Account Names”. In addition to the
CREATE USERstatement, you can issueGRANTstatements that give specific privileges to the account, although that is not necessary for the remaining steps in this procedure.Invoke the mysql client to connect to the server using the new account:
shell>
mysql -h ::1 -u ipv6user -pipv6passTry some simple statements that show connection information:
mysql>
STATUS... Connection: ::1 via TCP/IP ... mysql>SELECT CURRENT_USER(), @@bind_address;+----------------+----------------+ | CURRENT_USER() | @@bind_address | +----------------+----------------+ | ipv6user@::1 | :: | +----------------+----------------+
The following procedure shows how to configure MySQL to permit IPv6 connections by remote clients. It is similar to the preceding procedure for local clients, but the server and client hosts are distinct and each has its own nonlocal IPv6 address. The example uses these addresses:
Server host: 2001:db8:0:f101::1 Client host: 2001:db8:0:f101::2
These addresses are chosen from the nonroutable address range recommended by IANA for documentation purposes and suffice for testing on your local network. To accept IPv6 connections from clients outside the local network, the server host must have a public address. If your network provider assigns you an IPv6 address, you can use that. Otherwise, another way to obtain an address is to use an IPv6 broker; see Section 6.1.8.5, “Obtaining an IPv6 Address from a Broker”.
Start the MySQL server with an appropriate
--bind-addressoption to permit it to accept IPv6 connections. For example, put the following lines in your server option file and restart the server:[mysqld] bind-address = *
Alternatively, you can bind the server to
2001:db8:0:f101::1, but that makes the server more restrictive for TCP/IP connections. It accepts only IPv6 connections for that single address and rejects IPv4 connections. For more information, see Section 6.1.8.2, “Configuring the MySQL Server to Permit IPv6 Connections”.On the server host (
2001:db8:0:f101::1), create an account for a user who will connect from the client host (2001:db8:0:f101::2):mysql>
CREATE USER 'remoteipv6user'@'2001:db8:0:f101::2' IDENTIFIED BY 'remoteipv6pass';On the client host (
2001:db8:0:f101::2), invoke the mysql client to connect to the server using the new account:shell>
mysql -h 2001:db8:0:f101::1 -u remoteipv6user -premoteipv6passTry some simple statements that show connection information:
mysql>
STATUS... Connection: 2001:db8:0:f101::1 via TCP/IP ... mysql>SELECT CURRENT_USER(), @@bind_address;+-----------------------------------+----------------+ | CURRENT_USER() | @@bind_address | +-----------------------------------+----------------+ | remoteipv6user@2001:db8:0:f101::2 | :: | +-----------------------------------+----------------+
If you do not have a public IPv6 address that enables your system to communicate over IPv6 outside your local network, you can obtain one from an IPv6 broker. The Wikipedia IPv6 Tunnel Broker page lists several brokers and their features, such as whether they provide static addresses and the supported routing protocols.
After configuring your server host to use a broker-supplied IPv6
address, start the MySQL server with an appropriate
--bind-address option to permit
the server to accept IPv6 connections. For example, put the
following lines in the server option file and restart the
server:
[mysqld] bind-address = *
Alternatively, you can bind the server to the specific IPv6 address provided by the broker, but that makes the server more restrictive for TCP/IP connections. It accepts only IPv6 connections for that single address and rejects IPv4 connections. For more information, see Section 6.1.8.2, “Configuring the MySQL Server to Permit IPv6 Connections”. In addition, if the broker allocates dynamic addresses, the address provided for your system might change the next time you connect to the broker. If so, any accounts you create that name the original address become invalid. To bind to a specific address but avoid this change-of-address problem, you may be able to arrange with the broker for a static IPv6 address.
The following example shows how to use Freenet6 as the broker and the gogoc IPv6 client package on Gentoo Linux.
Create an account at Freenet6 by visiting this URL and signing up:
http://gogonet.gogo6.com
After creating the account, go to this URL, sign in, and create a user ID and password for the IPv6 broker:
http://gogonet.gogo6.com/page/freenet6-registration
As
root, install gogoc:shell>
emerge gogocEdit
/etc/gogoc/gogoc.confto set theuseridandpasswordvalues. For example:userid=gogouser passwd=gogopass
Start gogoc:
shell>
/etc/init.d/gogoc startTo start gogoc each time your system boots, execute this command:
shell>
rc-update add gogoc defaultUse ping6 to try to ping a host:
shell>
ping6 ipv6.google.comTo see your IPv6 address:
shell>
ifconfig tun
MySQL Server supports a HELP
statement that returns information from the MySQL Reference manual
(see Section 14.8.3, “HELP Syntax”). Several tables in the
mysql system database contain the information
needed to support this statement (see
Section 6.3, “The mysql System Database”). The proper operation of this
statement requires that these help tables be initialized, which is
done by processing the contents of the
fill_help_tables.sql script.
If you install MySQL using a binary or source distribution on Unix, help table content initialization occurs when you initialize the data directory (see Section 2.10.1, “Initializing the Data Directory”). For an RPM distribution on Linux or binary distribution on Windows, content initialization occurs as part of the MySQL installation process.
If you upgrade MySQL using a binary distribution, help table
content is not upgraded automatically, but you can upgrade it
manually. Locate the fill_help_tables.sql
file in the share or
share/mysql directory. Change location into
that directory and process the file with the
mysql client as follows:
shell> mysql -u root mysql < fill_help_tables.sql
You can also obtain the latest
fill_help_tables.sql at any time to upgrade
your help tables. Download the proper file for your version of
MySQL from http://dev.mysql.com/doc/index-other.html. After
downloading and uncompressing the file, process it with
mysql as described previously.
If you are working with Git and a MySQL development source tree,
you must use a downloaded copy of the
fill_help_tables.sql file because the source
tree contains only a “stub” version.
For a server that participates in replication, the help table content upgrade process involves multiple servers. For details, see Section 18.4.1.29, “Replication of Server-Side Help Tables”.
On Unix, signals can be sent to processes. mysqld responds to signals sent to it as follows:
SIGTERMcauses the server to shut down.SIGHUPcauses the server to reload the grant tables and to flush tables, logs, the thread cache, and the host cache. These actions are like various forms of theFLUSHstatement. The server also writes a status report to the error log that has this format:Status information: Current dir: /var/mysql/data/ Running threads: 0 Stack size: 196608 Current locks: Key caches: default Buffer_size: 8388600 Block_size: 1024 Division_limit: 100 Age_limit: 300 blocks used: 0 not flushed: 0 w_requests: 0 writes: 0 r_requests: 0 reads: 0 handler status: read_key: 0 read_next: 0 read_rnd 0 read_first: 1 write: 0 delete 0 update: 0 Table status: Opened tables: 5 Open tables: 0 Open files: 7 Open streams: 0 Alarm status: Active alarms: 1 Max used alarms: 2 Next alarm time: 67
The server shutdown process takes place as follows:
The shutdown process is initiated.
This can occur initiated several ways. For example, a user with the
SHUTDOWNprivilege can execute a mysqladmin shutdown command. mysqladmin can be used on any platform supported by MySQL. Other operating system-specific shutdown initiation methods are possible as well: The server shuts down on Unix when it receives aSIGTERMsignal. A server running as a service on Windows shuts down when the services manager tells it to.The server creates a shutdown thread if necessary.
Depending on how shutdown was initiated, the server might create a thread to handle the shutdown process. If shutdown was requested by a client, a shutdown thread is created. If shutdown is the result of receiving a
SIGTERMsignal, the signal thread might handle shutdown itself, or it might create a separate thread to do so. If the server tries to create a shutdown thread and cannot (for example, if memory is exhausted), it issues a diagnostic message that appears in the error log:Error: Can't create thread to kill server
The server stops accepting new connections.
To prevent new activity from being initiated during shutdown, the server stops accepting new client connections by closing the handlers for the network interfaces to which it normally listens for connections: the TCP/IP port, the Unix socket file, the Windows named pipe, and shared memory on Windows.
The server terminates current activity.
For each thread associated with a client connection, the server breaks the connection to the client and marks the thread as killed. Threads die when they notice that they are so marked. Threads for idle connections die quickly. Threads that currently are processing statements check their state periodically and take longer to die. For additional information about thread termination, see Section 14.7.6.4, “KILL Syntax”, in particular for the instructions about killed
REPAIR TABLEorOPTIMIZE TABLEoperations onMyISAMtables.For threads that have an open transaction, the transaction is rolled back. If a thread is updating a nontransactional table, an operation such as a multiple-row
UPDATEorINSERTmay leave the table partially updated because the operation can terminate before completion.If the server is a master replication server, it treats threads associated with currently connected slaves like other client threads. That is, each one is marked as killed and exits when it next checks its state.
If the server is a slave replication server, it stops the I/O and SQL threads, if they are active, before marking client threads as killed. The SQL thread is permitted to finish its current statement (to avoid causing replication problems), and then stops. If the SQL thread is in the middle of a transaction at this point, the server waits until the current replication event group (if any) has finished executing, or until the user issues a
KILL QUERYorKILL CONNECTIONstatement. See also Section 14.4.2.7, “STOP SLAVE Syntax”. Since nontransactional statements cannot be rolled back, in order to guarantee crash-safe replication, only transactional tables should be used.NoteTo guarantee crash safety on the slave, you must run the slave with
--relay-log-recoveryenabled.See also Section 18.2.4, “Replication Relay and Status Logs”).
The server shuts down or closes storage engines.
At this stage, the server flushes the table cache and closes all open tables.
Each storage engine performs any actions necessary for tables that it manages.
InnoDBflushes its buffer pool to disk (unlessinnodb_fast_shutdownis 2), writes the current LSN to the tablespace, and terminates its own internal threads.MyISAMflushes any pending index writes for a table.The server exits.
To provide information to management processes, the server returns one of the exit codes described in the following list. The phrase in parentheses indicates the action taken by systemd in response to the code, for platforms on which systemd is used to manage the server.
0 = successful termination (no restart done)
1 = unsuccessful termination (no restart done)
2 = unsuccessful termination (restart done)
The server returns the codes just described as of MySQL 5.7.6. Any management script written for older servers should be revised to handle three exit values if it checks only for 1 as a failure exit value.
Information managed by the MySQL server is stored under a directory known as the data directory. The following list briefly describes the items typically found in the data directory, with cross references for additional information:
Data directory subdirectories. Each subdirectory of the data directory is a database directory and corresponds to a database managed by the server. All MySQL installations have certain standard databases:
The
mysqldirectory corresponds to themysqlsystem database, which contains information required by the MySQL server as it runs. See Section 6.3, “The mysql System Database”.The
performance_schemadirectory corresponds to the Performance Schema, which provides information used to inspect the internal execution of the server at runtime. See Chapter 23, MySQL Performance Schema.The
sysdirectory corresponds to thesysschema, which provides a set of objects to help interpret Performance Schema information more easily. See Chapter 24, MySQL sys Schema.The
ndbinfodirectory corresponds to thendbinfodatabase that stores information specific to MySQL Cluster (present only for installations built to include MySQL Cluster). See Section 19.5.10, “The ndbinfo MySQL Cluster Information Database”.
Other subdirectories correspond to databases created by users or applications.
NoteINFORMATION_SCHEMAis a standard database, but its implementation uses no corresponding database directory.Log files written by the server. See Section 6.4, “MySQL Server Logs”.
InnoDBtablespace and log files. See Chapter 15, The InnoDB Storage Engine.Default/autogenerated SSL and RSA certificate and key files. See Section 7.4.6, “Creating SSL and RSA Certificates and Keys”.
The server process ID file (while the server is running).
Some items in the preceding list can be relocated elsewhere by
reconfigurating the server. In addition, the
datadir system variable enables
the location of the data directory itself to be discovered or
changed. For any given MySQL installation, check the server
configuration to determine whether items have been moved.
The mysql database is the system database. It
contains tables that store information required by the MySQL
server as it runs.
Tables in the mysql database fall into these
categories:
The remainder of this section enumerates the tables in each
category, with cross references for additional information. System
tables use the MyISAM storage engine unless
otherwise indicated.
These system tables contain grant information about user accounts and the privileges held by them:
For more information about the structure, contents, and purpose of the grant tables, see Section 7.2.2, “Grant Tables”.
These system tables contain information about stored programs, user-defined functions, and server-side plugins:
event: Information about Event Scheduler events. See Section 21.4, “Using the Event Scheduler”. The server loads events listed in this table during its startup sequence, unless started with the--skip-grant-tablesoption.func: Information about user-defined functions (UDFs). See Section 26.4, “Adding New Functions to MySQL”. The server loads UDFs listed in this table during its startup sequence, unless started with the--skip-grant-tablesoption.plugin: Information about server-side plugins. See Section 6.5.2, “Installing and Uninstalling Plugins”, and Section 26.2, “The MySQL Plugin API”. The server loads plugins listed in this table during its startup sequence, unless started with the--skip-grant-tablesoption.The
plugintable uses theInnoDBstorage engine as of MySQL 5.7.6,MyISAMbefore that.proc: Information about stored procedures and functions. See Section 21.2, “Using Stored Routines (Procedures and Functions)”.
The server uses these system tables for logging:
Log tables use the CSV storage engine.
For more information, see Section 6.4, “MySQL Server Logs”.
These system tables contain server-side help information:
These tables use the InnoDB storage engine as
of MySQL 5.7.5, MyISAM before that.
For more information, see Section 6.1.9, “Server-Side Help”.
These system tables contain time zone information:
These tables use the InnoDB storage engine as
of MySQL 5.7.5, MyISAM before that.
For more information, see Section 11.6, “MySQL Server Time Zone Support”.
The server uses these system tables to support replication:
gtid_executed: Table for storing GTID values. See mysql.gtid_executed Table.The
gtid_executedtable uses theInnoDBstorage engine.ndb_binlog_index: Binary log information for MySQL Cluster replication. See Section 19.6.4, “MySQL Cluster Replication Schema and Tables”.slave_master_info,slave_relay_log_info,slave_worker_info: Used to store replication information on slave servers. See Section 18.2.4, “Replication Relay and Status Logs”.These tables use the
InnoDBstorage engine.
These system tables are for use by the optimizer:
innodb_index_stats,innodb_table_stats: Used forInnoDBpersistent optimizer statistics. See Section 15.6.11.1, “Configuring Persistent Optimizer Statistics Parameters”.server_cost,engine_cost: The optimizer cost model uses tables that contain cost estimate information about operations that occur during query execution.server_costcontains optimizer cost estimates for general server operations.engine_costcontains estimates for operations specific to particular storage engines. See Section 9.9.5, “The Optimizer Cost Model”.
These tables use the InnoDB storage engine.
Other system tables do not fall into the preceding categories:
audit_log_filter,audit_log_user: If MySQL Enterprise Audit is installed, these tables provide persistent storage of audit log filter definitions and user accounts. See Section 7.5.4.7.1, “Audit Log Tables”.firewall_users,firewall_whitelist: If MySQL Enterprise Firewall is installed, these tables provide persistent storage for information used by the firewall. See Section 7.5.5, “MySQL Enterprise Firewall”.servers: Used by theFEDERATEDstorage engine. See Section 16.8.2.2, “Creating a FEDERATED Table Using CREATE SERVER”.The
serverstable uses theInnoDBstorage engine as of MySQL 5.7.6,MyISAMbefore that.
MySQL Server has several logs that can help you find out what activity is taking place.
| Log Type | Information Written to Log |
|---|---|
| Error log | Problems encountered starting, running, or stopping mysqld |
| General query log | Established client connections and statements received from clients |
| Binary log | Statements that change data (also used for replication) |
| Relay log | Data changes received from a replication master server |
| Slow query log | Queries that took more than
long_query_time seconds to
execute |
| DDL log (metadata log) | Metadata operations performed by DDL statements |
By default, no logs are enabled, except the error log on Windows. (The DDL log is always created when required, and has no user-configurable options; see Section 6.4.6, “The DDL Log”.) The following log-specific sections provide information about the server options that enable logging.
By default, the server writes files for all enabled logs in the data
directory. You can force the server to close and reopen the log
files (or in some cases switch to a new log file) by flushing the
logs. Log flushing occurs when you issue a
FLUSH LOGS
statement; execute mysqladmin with a
flush-logs or refresh
argument; or execute mysqldump with a
--flush-logs or
--master-data option. See
Section 14.7.6.3, “FLUSH Syntax”, Section 5.5.2, “mysqladmin — Client for Administering a MySQL Server”, and
Section 5.5.4, “mysqldump — A Database Backup Program”. In addition, the binary log is flushed
when its size reaches the value of the
max_binlog_size system variable.
You can control the general query and slow query logs during runtime. You can enable or disable logging, or change the log file name. You can tell the server to write general query and slow query entries to log tables, log files, or both. For details, see Section 6.4.1, “Selecting General Query and Slow Query Log Output Destinations”, Section 6.4.3, “The General Query Log”, and Section 6.4.5, “The Slow Query Log”.
The relay log is used only on slave replication servers, to hold data changes from the master server that must also be made on the slave. For discussion of relay log contents and configuration, see Section 18.2.4.1, “The Slave Relay Log”.
For information about log maintenance operations such as expiration of old log files, see Section 6.4.7, “Server Log Maintenance”.
For information about keeping logs secure, see Section 7.1.2.3, “Passwords and Logging”.
MySQL Server provides flexible control over the destination of
output to the general query log and the slow query log, if those
logs are enabled. Possible destinations for log entries are log
files or the general_log and
slow_log tables in the mysql
database. Either or both destinations can be selected.
Log control at server startup.
The --log-output option specifies
the destination for log output. This option does not in itself
enable the logs. Its syntax is
--log-output[=:
value,...]
If
--log-outputis given with a value, the value should be a comma-separated list of one or more of the wordsTABLE(log to tables),FILE(log to files), orNONE(do not log to tables or files).NONE, if present, takes precedence over any other specifiers.If
--log-outputis omitted, the default logging destination isFILE.
The general_log system variable
controls logging to the general query log for the selected log
destinations. If specified at server startup,
general_log takes an optional
argument of 1 or 0 to enable or disable the log. To specify a file
name other than the default for file logging, set the
general_log_file variable.
Similarly, the slow_query_log
variable controls logging to the slow query log for the selected
destinations and setting
slow_query_log_file specifies a
file name for file logging. If either log is enabled, the server
opens the corresponding log file and writes startup messages to
it. However, further logging of queries to the file does not occur
unless the FILE log destination is selected.
Examples:
To write general query log entries to the log table and the log file, use
--log-output=TABLE,FILEto select both log destinations and--general_logto enable the general query log.To write general and slow query log entries only to the log tables, use
--log-output=TABLEto select tables as the log destination and--general_logand--slow_query_logto enable both logs.To write slow query log entries only to the log file, use
--log-output=FILEto select files as the log destination and--slow_query_logto enable the slow query log. (In this case, because the default log destination isFILE, you could omit the--log-outputoption.)
Log control at runtime. The system variables associated with log tables and files enable runtime control over logging:
The global
log_outputsystem variable indicates the current logging destination. It can be modified at runtime to change the destination.The global
general_logandslow_query_logvariables indicate whether the general query log and slow query log are enabled (ON) or disabled (OFF). You can set these variables at runtime to control whether the logs are enabled.The global
general_log_fileandslow_query_log_filevariables indicate the names of the general query log and slow query log files. You can set these variables at server startup or at runtime to change the names of the log files.To disable or enable general query logging for the current connection, set the session
sql_log_offvariable toONorOFF.
The use of tables for log output offers the following benefits:
Log entries have a standard format. To display the current structure of the log tables, use these statements:
SHOW CREATE TABLE mysql.general_log; SHOW CREATE TABLE mysql.slow_log;
Log contents are accessible through SQL statements. This enables the use of queries that select only those log entries that satisfy specific criteria. For example, to select log contents associated with a particular client (which can be useful for identifying problematic queries from that client), it is easier to do this using a log table than a log file.
Logs are accessible remotely through any client that can connect to the server and issue queries (if the client has the appropriate log table privileges). It is not necessary to log in to the server host and directly access the file system.
The log table implementation has the following characteristics:
In general, the primary purpose of log tables is to provide an interface for users to observe the runtime execution of the server, not to interfere with its runtime execution.
CREATE TABLE,ALTER TABLE, andDROP TABLEare valid operations on a log table. ForALTER TABLEandDROP TABLE, the log table cannot be in use and must be disabled, as described later.By default, the log tables use the
CSVstorage engine that writes data in comma-separated values format. For users who have access to the.CSVfiles that contain log table data, the files are easy to import into other programs such as spreadsheets that can process CSV input.The log tables can be altered to use the
MyISAMstorage engine. You cannot useALTER TABLEto alter a log table that is in use. The log must be disabled first. No engines other thanCSVorMyISAMare legal for the log tables.To disable logging so that you can alter (or drop) a log table, you can use the following strategy. The example uses the general query log; the procedure for the slow query log is similar but uses the
slow_logtable andslow_query_logsystem variable.SET @old_log_state = @@global.general_log; SET GLOBAL general_log = 'OFF'; ALTER TABLE mysql.general_log ENGINE = MyISAM; SET GLOBAL general_log = @old_log_state;
TRUNCATE TABLEis a valid operation on a log table. It can be used to expire log entries.RENAME TABLEis a valid operation on a log table. You can atomically rename a log table (to perform log rotation, for example) using the following strategy:USE mysql; DROP TABLE IF EXISTS general_log2; CREATE TABLE general_log2 LIKE general_log; RENAME TABLE general_log TO general_log_backup, general_log2 TO general_log;
CHECK TABLEis a valid operation on a log table.LOCK TABLEScannot be used on a log table.INSERT,DELETE, andUPDATEcannot be used on a log table. These operations are permitted only internally to the server itself.FLUSH TABLES WITH READ LOCKand the state of theread_onlysystem variable have no effect on log tables. The server can always write to the log tables.Entries written to the log tables are not written to the binary log and thus are not replicated to slave servers.
To flush the log tables or log files, use
FLUSH TABLESorFLUSH LOGS, respectively.Partitioning of log tables is not permitted.
A mysqldump dump includes statements to recreate those tables so that they are not missing after reloading the dump file. Log table contents are not dumped.
The error log contains information indicating when mysqld was started and stopped and also any critical errors that occur while the server is running. If mysqld notices a table that needs to be automatically checked or repaired, it writes a message to the error log.
On some operating systems, the error log contains a stack trace if mysqld exits abnormally. The trace can be used to determine where mysqld exited. See Section 26.5, “Debugging and Porting MySQL”.
If mysqld_safe is used to start
mysqld and mysqld exits
abnormally, mysqld_safe notices this, restarts
mysqld, and writes a mysqld
restarted message to the error log.
In the following discussion, “console” means
stderr, the standard error output; this is your
terminal or console window unless the standard error output has
been redirected.
On Windows, the --log-error,
--pid-file, and
--console options affect error
logging:
If no log file name is specified, the default log file is
host_name.err--pid-fileoption is specified. In that case, the default name is the PID file base name with a suffix of.errin the data directory.Without
--log-error, mysqld writes error messages to the default log file.With
--log-error[=, mysqld writes error messages to an error log file. mysqld writes to the named file if present, creating it in the data directory unless an absolute path name is given to specify a different directory. If no file is named, mysqld writes to the default log file.file_name]With
--console, mysqld writes error messages to the console.--log-error, if given, is ignored and has no effect. If both options are present, their order does not matter:--consoletakes precedence and error messages go to the console. (In MySQL 5.5 and 5.6, the precedence is reversed:--log-errorcauses--consoleto be ignored.)
In addition, on Windows, the server by default writes events and
error messages to the Windows Event Log within the Application
log. Entries marked as Error,
Warning, and Note are
written to the Event Log, but not informational messages such as
information statements from individual storage engines. These log
entries have a source of MySQL. As of MySQL
5.7.5, information written to the Windows Event Log can be
controlled using the log_syslog
system variable, as described later.
On Unix and Unix-like systems, mysqld writes error log messages as follows:
Without
--log-error, mysqld writes error messages to the console.With
--log-error[=, mysqld writes error messages to an error log file. The server uses the named file if present, creating it in the data directory unless an absolute path name is given to specify a different directory. If no file is named, the default name isfile_name]host_name.errNoteIt is common for Yum or APT package installations to configure the error log location to be under
/var/logwith an entry likelog-error=/var/log/mysqld.login a server configuration file; removing the file name from the entry reverts the error log file to its default setting, which ishost_name.err
At runtime, if the server writes error messages to the console, it
sets the log_error system
variable to stderr. Otherwise,
log_error indicates the error log
file name. In particular, on Windows,
--console overrides use of an error
log file and sends error messages to the console, so the server
sets log_error to
stderr. This occurs even if
--log-error is also given.
If you specify --log-error in an
option file in a [mysqld],
[server], or [mysqld_safe]
section, mysqld_safe will find and use the
option.
Using Syslog for the Error Log
On Unix and Unix-like systems, it is possible to write the error
log to syslog. To control logging to
syslog in MySQL 5.7.5 or later, use these
system variables:
log_syslog: Enable this variable to send the error log tosyslog. In this case, the following system variables can also be used for finer control.log_syslog_facility: The default facility forsyslogmessages isdaemon. Set this variable to specify a different facility.log_syslog_include_pid: Whether to include the server process ID in each line ofsyslogoutput.log_syslog_tag: This variable defines a tag to add to the server identifier (mysqld) insyslogmessages. If defined, the tag is appended to the identifier with a leading hyphen.
Before MySQL 5.7.5, control of output to syslog
is available only on Unix and Unix-like systems and is handled by
mysqld_safe, which captures server error output
and passes it to syslog. (On Windows, logging
to the Event Log is enabled by default and cannot be disabled.)
As of MySQL 5.7.5, using mysqld_safe for
syslog error logging is deprecated; you
should use the server system variables instead.
mysqld_safe has three error-logging options,
--syslog,
--skip-syslog,
and --log-error. The default
with no logging options or with
--skip-syslog
is to use the default log file. To explicitly specify use of an
error log file, specify
--log-error=
to mysqld_safe, and
mysqld_safe will arrange for
mysqld to write messages to a log file. To use
file_namesyslog instead, specify the
--syslog option. For
syslog output, a tag can be specified with
--syslog-tag=;
this is appended to the tag_valmysqld server
identifier with a leading hyphen.
Error Log Verbosity
As of MySQL 5.7.2, the
log_error_verbosity system
variable controls verbosity of the server in writing error,
warning, and note messages to the error log. Permitted values are
1 (errors only), 2 (errors and warnings), 3 (errors, warnings, and
notes), with a default of 3. If the value is greater than 2, the
server logs aborted connections and access-denied errors for new
connection attempts. See Section B.5.2.11, “Communication Errors and Aborted Connections”.
Before MySQL 5.7.2, the
log_warnings system variable can
be used to control warning logging to the error log. By default,
log_warnings is enabled
(nonzero). Warning logging can be disabled using a value of 0. The
server logs messages about statements that are unsafe for
statement-based logging if the value is greater than 0, and logs
aborted connections and access-denied errors for new connection
attempts if the value is greater than 1. See
Section B.5.2.11, “Communication Errors and Aborted Connections”.
Error Log Message Format
As of MySQL 5.7.2, the
log_timestamps system variable
controls the timestamp time zone of messages written to the error
log (as well as to general query log and slow query log files).
Permitted values are UTC (the default) and
SYSTEM (local system time zone). Before MySQL
5.7.2, messages use the local system time zone.
As of MySQL 5.7.2, the ID included in error log messages is that of the thread within mysqld responsible for writing the message. This indicates which part of the server produced the message, and is consistent with general query log and slow query log messages, which include the connection thread ID. Before MySQL 5.7.2, the ID in error log messages is that of the mysqld process ID.
Flushing and Renaming the Error Log File
If you flush the logs using
FLUSH LOGS or
mysqladmin flush-logs and
mysqld is writing the error log to a file (for
example, if it was started with the
--log-error option), the server
closes and reopens the log file. To rename the file, do so
manually before flushing. Then flushing the logs reopens a new
file with the original file name. For example, you can rename the
file and create a new one using the following commands:
shell>mvshell>host_name.errhost_name.err-oldmysqladmin flush-logsshell>mvhost_name.err-oldbackup-directory
On Windows, use rename rather than mv.
If the server is not writing to a named file, no error log renaming occurs when the logs are flushed.
The general query log is a general record of what mysqld is doing. The server writes information to this log when clients connect or disconnect, and it logs each SQL statement received from clients. The general query log can be very useful when you suspect an error in a client and want to know exactly what the client sent to mysqld.
As of MySQL 5.7.8, each line that shows when a client connects
also includes using
to indicate
the protocol used to establish the connection.
connection_typeconnection_type is one of
TCP/IP (TCP/IP connection established without
SSL), SSL/TLS (TCP/IP connection established
with SSL), Socket (Unix socket file
connection), Named Pipe (Windows named pipe
connection), or Shared Memory (Windows shared
memory connection).
mysqld writes statements to the query log in the order that it receives them, which might differ from the order in which they are executed. This logging order is in contrast with that of the binary log, for which statements are written after they are executed but before any locks are released. In addition, the query log may contain statements that only select data while such statements are never written to the binary log.
When using statement-based binary logging on a replication master server, statements received by its slaves are written to the query log of each slave. Statements are written to the query log of the master server if a client reads events with the mysqlbinlog utility and passes them to the server.
However, when using row-based binary logging, updates are sent as
row changes rather than SQL statements, and thus these statements
are never written to the query log when
binlog_format is
ROW. A given update also might not be written
to the query log when this variable is set to
MIXED, depending on the statement used. See
Section 18.2.1.1, “Advantages and Disadvantages of Statement-Based and Row-Based
Replication”, for more information.
By default, the general query log is disabled. To specify the
initial general query log state explicitly, use
--general_log[={0|1}]. With no
argument or an argument of 1,
--general_log enables the log. With
an argument of 0, this option disables the log. To specify a log
file name, use
--general_log_file=.
To specify the log destination, use
file_name--log-output (as described in
Section 6.4.1, “Selecting General Query and Slow Query Log Output Destinations”).
If you specify no name for the general query log file, the default
name is
host_name.log
To disable or enable the general query log or change the log file
name at runtime, use the global
general_log and
general_log_file system
variables. Set general_log to 0
(or OFF) to disable the log or to 1 (or
ON) to enable it. Set
general_log_file to specify the
name of the log file. If a log file already is open, it is closed
and the new file is opened.
When the general query log is enabled, the server writes output to
any destinations specified by the
--log-output option or
log_output system variable. If
you enable the log, the server opens the log file and writes
startup messages to it. However, further logging of queries to the
file does not occur unless the FILE log
destination is selected. If the destination is
NONE, the server writes no queries even if the
general log is enabled. Setting the log file name has no effect on
logging if the log destination value does not contain
FILE.
Server restarts and log flushing do not cause a new general query log file to be generated (although flushing closes and reopens it). To rename the file and create a new one, use the following commands:
shell>mvshell>host_name.loghost_name-old.logmysqladmin flush-logsshell>mvhost_name-old.logbackup-directory
On Windows, use rename rather than mv.
You can also rename the general query log file at runtime by disabling the log:
SET GLOBAL general_log = 'OFF';
With the log disabled, rename the log file externally; for example, from the command line. Then enable the log again:
SET GLOBAL general_log = 'ON';
This method works on any platform and does not require a server restart.
The session sql_log_off variable
can be set to ON or OFF to
disable or enable general query logging for the current
connection.
Passwords in statements written to the general query log are
rewritten by the server not to occur literally in plain text.
Password rewriting can be suppressed for the general query log by
starting the server with the
--log-raw option. This option may
be useful for diagnostic purposes, to see the exact text of
statements as received by the server, but for security reasons is
not recommended for production use. See also
Section 7.1.2.3, “Passwords and Logging”.
An implication of password rewriting is that statements that
cannot be parsed (due, for example, to syntax errors) are not
written to the general query log because they cannot be known to
be password free. Use cases that require logging of all statements
including those with errors should use the
--log-raw option, bearing in mind
that this also bypasses password rewriting.
Password rewriting occurs only when plain text passwords are expected. For statements with syntax that expect a password hash value, no rewriting occurs. If a plain text password is supplied erroneously for such syntax, the password is logged as given, without rewriting. For example, the following statement is logged as shown because a password hash value is expected:
CREATE USER 'user1'@'localhost' IDENTIFIED BY PASSWORD 'not-so-secret';
As of MySQL 5.7.2, the
log_timestamps system variable
controls the timestamp time zone of messages written to the
general query log file (as well as to the slow query log file and
the error log). It does not affect the time zone of general query
log and slow query log messages written to log tables, but rows
retrieved from those tables can be converted from the local system
time zone to any desired time zone with
CONVERT_TZ() or by setting the
session time_zone system
variable. Before MySQL 5.7.2, messages use the local system time
zone.
The binary log contains “events” that describe
database changes such as table creation operations or changes to
table data. It also contains events for statements that
potentially could have made changes (for example, a
DELETE which matched no rows),
unless row-based logging is used. The binary log also contains
information about how long each statement took that updated data.
The binary log has two important purposes:
For replication, the binary log on a master replication server provides a record of the data changes to be sent to slave servers. The master server sends the events contained in its binary log to its slaves, which execute those events to make the same data changes that were made on the master. See Section 18.2, “Replication Implementation”.
Certain data recovery operations require use of the binary log. After a backup has been restored, the events in the binary log that were recorded after the backup was made are re-executed. These events bring databases up to date from the point of the backup. See Section 8.5, “Point-in-Time (Incremental) Recovery Using the Binary Log”.
The binary log is not used for statements such as
SELECT or
SHOW that do not modify data. To
log all statements (for example, to identify a problem query), use
the general query log. See Section 6.4.3, “The General Query Log”.
Running a server with binary logging enabled makes performance slightly slower. However, the benefits of the binary log in enabling you to set up replication and for restore operations generally outweigh this minor performance decrement.
The binary log is generally resilient to unexpected halts because only complete transactions are logged or read back. See Section 18.3.2, “Handling an Unexpected Halt of a Replication Slave” for more information.
Passwords in statements written to the binary log are rewritten by the server not to occur literally in plain text. See also Section 7.1.2.3, “Passwords and Logging”.
The following discussion describes some of the server options and variables that affect the operation of binary logging. For a complete list, see Section 18.1.6.4, “Binary Logging Options and Variables”.
To enable the binary log, start the server with the
--log-bin[=
option. If no base_name]base_name value is given,
the default name is the value of the pid-file
option (which by default is the name of host machine) followed by
-bin. If the base name is given, the server
writes the file in the data directory unless the base name is
given with a leading absolute path name to specify a different
directory. It is recommended that you specify a base name
explicitly rather than using the default of the host name; see
Section B.5.7, “Known Issues in MySQL”, for the reason.
If you supply an extension in the log name (for example,
--log-bin=),
the extension is silently removed and ignored.
base_name.extension
mysqld appends a numeric extension to the
binary log base name to generate binary log file names. The number
increases each time the server creates a new log file, thus
creating an ordered series of files. The server creates a new file
in the series each time it starts or flushes the logs. The server
also creates a new binary log file automatically after the current
log's size reaches
max_binlog_size. A binary log
file may become larger than
max_binlog_size if you are using
large transactions because a transaction is written to the file in
one piece, never split between files.
To keep track of which binary log files have been used,
mysqld also creates a binary log index file
that contains the names of all used binary log files. By default,
this has the same base name as the binary log file, with the
extension '.index'. You can change the name of
the binary log index file with the
--log-bin-index[=
option. You should not manually edit this file while
mysqld is running; doing so would confuse
mysqld.
file_name]
The term “binary log file” generally denotes an individual numbered file containing database events. The term “binary log” collectively denotes the set of numbered binary log files plus the index file.
A client that has the SUPER
privilege can disable binary logging of its own statements by
using a SET sql_log_bin=0 statement. See
Section 6.1.4, “Server System Variables”.
By default, the server logs the length of the event as well as the
event itself and uses this to verify that the event was written
correctly. You can also cause the server to write checksums for
the events by setting the
binlog_checksum system variable.
When reading back from the binary log, the master uses the event
length by default, but can be made to use checksums if available
by enabling the
master_verify_checksum system
variable. The slave I/O thread also verifies events received from
the master. You can cause the slave SQL thread to use checksums if
available when reading from the relay log by enabling the
slave_sql_verify_checksum system
variable.
The format of the events recorded in the binary log is dependent on the binary logging format. Three format types are supported, row-based logging, statement-based logging and mixed-base logging. The binary logging format used depends on the MySQL version. For general descriptions of the logging formats, see Section 6.4.4.1, “Binary Logging Formats”. For detailed information about the format of the binary log, see MySQL Internals: The Binary Log.
The server evaluates the
--binlog-do-db and
--binlog-ignore-db options in the
same way as it does the
--replicate-do-db and
--replicate-ignore-db options. For
information about how this is done, see
Section 18.2.5.1, “Evaluation of Database-Level Replication and Binary Logging Options”.
A replication slave server by default does not write to its own
binary log any data modifications that are received from the
replication master. To log these modifications, start the slave
with the --log-slave-updates option
in addition to the --log-bin option
(see Section 18.1.6.3, “Replication Slave Options and Variables”). This is done
when a slave is also to act as a master to other slaves in chained
replication.
You can delete all binary log files with the
RESET MASTER statement, or a subset
of them with PURGE BINARY LOGS. See
Section 14.7.6.6, “RESET Syntax”, and Section 14.4.1.1, “PURGE BINARY LOGS Syntax”.
If you are using replication, you should not delete old binary log
files on the master until you are sure that no slave still needs
to use them. For example, if your slaves never run more than three
days behind, once a day you can execute mysqladmin
flush-logs on the master and then remove any logs that
are more than three days old. You can remove the files manually,
but it is preferable to use PURGE BINARY
LOGS, which also safely updates the binary log index
file for you (and which can take a date argument). See
Section 14.4.1.1, “PURGE BINARY LOGS Syntax”.
You can display the contents of binary log files with the mysqlbinlog utility. This can be useful when you want to reprocess statements in the log for a recovery operation. For example, you can update a MySQL server from the binary log as follows:
shell> mysqlbinlog log_file | mysql -h server_name
mysqlbinlog also can be used to display replication slave relay log file contents because they are written using the same format as binary log files. For more information on the mysqlbinlog utility and how to use it, see Section 5.6.7, “mysqlbinlog — Utility for Processing Binary Log Files”. For more information about the binary log and recovery operations, see Section 8.5, “Point-in-Time (Incremental) Recovery Using the Binary Log”.
Binary logging is done immediately after a statement or transaction completes but before any locks are released or any commit is done. This ensures that the log is logged in commit order.
Updates to nontransactional tables are stored in the binary log immediately after execution.
Within an uncommitted transaction, all updates
(UPDATE,
DELETE, or
INSERT) that change transactional
tables such as InnoDB tables are cached until a
COMMIT statement is received by the
server. At that point, mysqld writes the entire
transaction to the binary log before the
COMMIT is executed.
Modifications to nontransactional tables cannot be rolled back. If
a transaction that is rolled back includes modifications to
nontransactional tables, the entire transaction is logged with a
ROLLBACK
statement at the end to ensure that the modifications to those
tables are replicated.
When a thread that handles the transaction starts, it allocates a
buffer of binlog_cache_size to
buffer statements. If a statement is bigger than this, the thread
opens a temporary file to store the transaction. The temporary
file is deleted when the thread ends.
The Binlog_cache_use status
variable shows the number of transactions that used this buffer
(and possibly a temporary file) for storing statements. The
Binlog_cache_disk_use status
variable shows how many of those transactions actually had to use
a temporary file. These two variables can be used for tuning
binlog_cache_size to a large
enough value that avoids the use of temporary files.
The max_binlog_cache_size system
variable (default 4GB, which is also the maximum) can be used to
restrict the total size used to cache a multiple-statement
transaction. If a transaction is larger than this many bytes, it
fails and rolls back. The minimum value is 4096.
If you are using the binary log and row based logging, concurrent
inserts are converted to normal inserts for CREATE ...
SELECT or
INSERT ...
SELECT statements. This is done to ensure that you can
re-create an exact copy of your tables by applying the log during
a backup operation. If you are using statement-based logging, the
original statement is written to the log.
The binary log format has some known limitations that can affect recovery from backups. See Section 18.4.1, “Replication Features and Issues”.
Binary logging for stored programs is done as described in Section 21.7, “Binary Logging of Stored Programs”.
Note that the binary log format differs in MySQL 5.7 from previous versions of MySQL, due to enhancements in replication. See Section 18.4.2, “Replication Compatibility Between MySQL Versions”.
Writes to the binary log file and binary log index file are
handled in the same way as writes to MyISAM
tables. See Section B.5.3.4, “How MySQL Handles a Full Disk”.
As of MySQL 5.7.7, the binary log is synchronized to disk at each
write by default (sync_binlog=1).
Prior to MySQL 5.7.7, it is not
(sync_binlog=0). So, prior to
MySQL 5.7.7, if the operating system or machine (not only the
MySQL server) crashes, there is a chance that the last statements
of the binary log are lost. To prevent this, use the
sync_binlog system variable to
synchronize the binary log to disk after every
N commit groups. See
Section 6.1.4, “Server System Variables”. The safest value for
sync_binlog is 1, but this is
also the slowest. Even with
sync_binlog set to 1, there is
still the chance of inconsistency between the table content and
binary log content in case of a crash.
For example, if you are using InnoDB tables and
the MySQL server processes a COMMIT
statement, it writes many prepared transactions to the binary log
in sequence, synchronizes the binary log, and then commits this
transaction into InnoDB. If the server crashes
between those two operations, the transaction is rolled back by
InnoDB at restart but still exists in the
binary log. Such an issue is resolved assuming
--innodb_support_xa is set to 1,
the default. Although this option is related to the support of XA
transactions in InnoDB, it also ensures that
the binary log and InnoDB data files are synchronized. For this
option to provide a greater degree of safety, the MySQL server
should also be configured to synchronize the binary log and the
InnoDB logs to disk before committing the
transaction. The InnoDB logs are synchronized
by default, and sync_binlog=1 can be used to
synchronize the binary log. The effect of this option is that at
restart after a crash, after doing a rollback of transactions, the
MySQL server removes rolled back InnoDB
transactions from the binary log. This ensures that the binary log
reflects the exact data of InnoDB tables, and
therefore the slave remains in synchrony with the master because
it does not receive a statement which has been rolled back.
innodb_support_xa is deprecated
and will be removed in a future release.
InnoDB support for two-phase commit in XA
transactions is always enabled as of MySQL 5.7.10.
If the MySQL server discovers at crash recovery that the binary
log is shorter than it should have been, it lacks at least one
successfully committed InnoDB transaction. This
should not happen if sync_binlog=1 and the
disk/file system do an actual sync when they are requested to
(some do not), so the server prints an error message The
binary log . In this case, this binary log is not
correct and replication should be restarted from a fresh snapshot
of the master's data.
file_name is shorter than
its expected size
The session values of the following system variables are written to the binary log and honored by the replication slave when parsing the binary log:
sql_mode(except that theNO_DIR_IN_CREATEmode is not replicated; see Section 18.4.1.38, “Replication and Variables”)
The server uses several logging formats to record information in the binary log. The exact format employed depends on the version of MySQL being used. There are three logging formats:
Replication capabilities in MySQL originally were based on propagation of SQL statements from master to slave. This is called statement-based logging. You can cause this format to be used by starting the server with
--binlog-format=STATEMENT.In row-based logging, the master writes events to the binary log that indicate how individual table rows are affected. It is important therefore that tables always use a primary key to ensure rows can be efficiently identified. You can cause the server to use row-based logging by starting it with
--binlog-format=ROW.A third option is also available: mixed logging. With mixed logging, statement-based logging is used by default, but the logging mode switches automatically to row-based in certain cases as described below. You can cause MySQL to use mixed logging explicitly by starting mysqld with the option
--binlog-format=MIXED.
Prior to MySQL 5.7.7, statement-based logging format was the default. In MySQL 5.7.7 and later, row-based logging format is the default.
The logging format can also be set or limited by the storage engine being used. This helps to eliminate issues when replicating certain statements between a master and slave which are using different storage engines.
With statement-based replication, there may be issues with replicating nondeterministic statements. In deciding whether or not a given statement is safe for statement-based replication, MySQL determines whether it can guarantee that the statement can be replicated using statement-based logging. If MySQL cannot make this guarantee, it marks the statement as potentially unreliable and issues the warning, Statement may not be safe to log in statement format.
You can avoid these issues by using MySQL's row-based replication instead.
You can select the binary logging format explicitly by starting
the MySQL server with
--binlog-format=.
The supported values for typetype are:
STATEMENTcauses logging to be statement based.ROWcauses logging to be row based.MIXEDcauses logging to use mixed format.
Prior to MySQL 5.7.7, statement-based logging format was the default. In MySQL 5.7.7 and later, row-based logging format is the default.
The logging format also can be switched at runtime. To specify
the format globally for all clients, set the global value of the
binlog_format system variable:
mysql>SET GLOBAL binlog_format = 'STATEMENT';mysql>SET GLOBAL binlog_format = 'ROW';mysql>SET GLOBAL binlog_format = 'MIXED';
An individual client can control the logging format for its own
statements by setting the session value of
binlog_format:
mysql>SET SESSION binlog_format = 'STATEMENT';mysql>SET SESSION binlog_format = 'ROW';mysql>SET SESSION binlog_format = 'MIXED';
Each MySQL Server can set its own and only its own binary
logging format (true whether
binlog_format is set with
global or session scope). This means that changing the logging
format on a replication master does not cause a slave to
change its logging format to match. (When using
STATEMENT mode, the
binlog_format system variable
is not replicated; when using MIXED or
ROW logging mode, it is replicated but is
ignored by the slave.) Changing the binary logging format on
the master while replication is ongoing, or without also
changing it on the slave can cause replication to fail with
errors such as Error executing row event: 'Cannot
execute statement: impossible to write to binary log since
statement is in row format and BINLOG_FORMAT =
STATEMENT.'
To change the global or session
binlog_format value, you must
have the SUPER privilege.
There are several reasons why a client might want to set binary logging on a per-session basis:
A session that makes many small changes to the database might want to use row-based logging.
A session that performs updates that match many rows in the
WHEREclause might want to use statement-based logging because it will be more efficient to log a few statements than many rows.Some statements require a lot of execution time on the master, but result in just a few rows being modified. It might therefore be beneficial to replicate them using row-based logging.
There are exceptions when you cannot switch the replication format at runtime:
From within a stored function or a trigger
If the
NDBstorage engine is enabledIf the session is currently in row-based replication mode and has open temporary tables
Trying to switch the format in any of these cases results in an error.
If you are using InnoDB tables and
the transaction isolation level is READ
COMMITTED or READ
UNCOMMITTED, only row-based logging can be used. It is
possible to change the logging format to
STATEMENT, but doing so at runtime leads very
rapidly to errors because InnoDB can no
longer perform inserts.
Switching the replication format at runtime is not recommended
when any temporary tables exist, because temporary tables are
logged only when using statement-based replication, whereas with
row-based replication they are not logged. With mixed
replication, temporary tables are usually logged; exceptions
happen with user-defined functions (UDFs) and with the
UUID() function.
With the binary log format set to ROW, many
changes are written to the binary log using the row-based
format. Some changes, however, still use the statement-based
format. Examples include all DDL (data definition language)
statements such as CREATE TABLE,
ALTER TABLE, or
DROP TABLE.
The --binlog-row-event-max-size
option is available for servers that are capable of row-based
replication. Rows are stored into the binary log in chunks
having a size in bytes not exceeding the value of this option.
The value must be a multiple of 256. The default value is 8192.
When using statement-based logging for replication, it is possible for the data on the master and slave to become different if a statement is designed in such a way that the data modification is nondeterministic; that is, it is left to the will of the query optimizer. In general, this is not a good practice even outside of replication. For a detailed explanation of this issue, see Section B.5.7, “Known Issues in MySQL”.
For information about logs kept by replication slaves, see Section 18.2.4, “Replication Relay and Status Logs”.
When running in MIXED logging format, the
server automatically switches from statement-based to row-based
logging under the following conditions:
When a function contains
UUID().When one or more tables with
AUTO_INCREMENTcolumns are updated and a trigger or stored function is invoked. Like all other unsafe statements, this generates a warning ifbinlog_format = STATEMENT.For more information, see Section 18.4.1.1, “Replication and AUTO_INCREMENT”.
When the body of a view requires row-based replication, the statement creating the view also uses it. For example, this occurs when the statement creating a view uses the
UUID()function.When a call to a UDF is involved.
If a statement is logged by row and the session that executed the statement has any temporary tables, logging by row is used for all subsequent statements (except for those accessing temporary tables) until all temporary tables in use by that session are dropped.
This is true whether or not any temporary tables are actually logged.
Temporary tables cannot be logged using row-based format; thus, once row-based logging is used, all subsequent statements using that table are unsafe. The server approximates this condition by treating all statements executed during the session as unsafe until the session no longer holds any temporary tables.
When
FOUND_ROWS()orROW_COUNT()is used. (Bug #12092, Bug #30244)When
USER(),CURRENT_USER(), orCURRENT_USERis used. (Bug #28086)When a statement refers to one or more system variables. (Bug #31168)
Exception. The following system variables, when used with session scope (only), do not cause the logging format to switch:
For information about determining system variable scope, see Section 6.1.5, “Using System Variables”.
For information about how replication treats
sql_mode, see Section 18.4.1.38, “Replication and Variables”.When one of the tables involved is a log table in the
mysqldatabase.When the
LOAD_FILE()function is used. (Bug #39701)
A warning is generated if you try to execute a statement using
statement-based logging that should be written using row-based
logging. The warning is shown both in the client (in the
output of SHOW WARNINGS) and
through the mysqld error log. A warning is
added to the SHOW WARNINGS
table each time such a statement is executed. However, only
the first statement that generated the warning for each client
session is written to the error log to prevent flooding the
log.
In addition to the decisions above, individual engines can also determine the logging format used when information in a table is updated. The logging capabilities of an individual engine can be defined as follows:
If an engine supports row-based logging, the engine is said to be row-logging capable.
If an engine supports statement-based logging, the engine is said to be statement-logging capable.
A given storage engine can support either or both logging formats. The following table lists the formats supported by each engine.
| Storage Engine | Row Logging Supported | Statement Logging Supported |
|---|---|---|
ARCHIVE | Yes | Yes |
BLACKHOLE | Yes | Yes |
CSV | Yes | Yes |
EXAMPLE | Yes | No |
FEDERATED | Yes | Yes |
HEAP | Yes | Yes |
InnoDB | Yes | Yes when the transaction isolation level is
REPEATABLE READ or
SERIALIZABLE; No
otherwise. |
MyISAM | Yes | Yes |
MERGE | Yes | Yes |
NDB | Yes | No |
Whether a statement is to be logged and the logging mode to be
used is determined according to the type of statement (safe,
unsafe, or binary injected), the binary logging format
(STATEMENT, ROW, or
MIXED), and the logging capabilities of the
storage engine (statement capable, row capable, both, or
neither). (Binary injection refers to logging a change that must
be logged using ROW format.)
Statements may be logged with or without a warning; failed statements are not logged, but generate errors in the log. This is shown in the following decision table, where SLC stands for “statement-logging capable” and RLC stands for “row-logging capable”.
| Condition | Action | ||||
|---|---|---|---|---|---|
| Type | binlog_format | SLC | RLC | Error / Warning | Logged as |
| * | * | No | No | Error: Cannot execute statement: Binary logging is impossible since at least one engine is involved that is both row-incapable and statement-incapable. | - |
| Safe | STATEMENT | Yes | No | - | STATEMENT |
| Safe | MIXED | Yes | No | - | STATEMENT |
| Safe | ROW | Yes | No | Error: Cannot execute statement: Binary logging
is impossible since BINLOG_FORMAT =
ROW and at least one table uses a storage
engine that is not capable of row-based logging. | - |
| Unsafe | STATEMENT | Yes | No | Warning: Unsafe statement binlogged in statement
format, since BINLOG_FORMAT =
STATEMENT | STATEMENT |
| Unsafe | MIXED | Yes | No | Error: Cannot execute statement: Binary logging
of an unsafe statement is impossible when the storage
engine is limited to statement-based logging, even if
BINLOG_FORMAT = MIXED. | - |
| Unsafe | ROW | Yes | No | Error: Cannot execute statement: Binary logging
is impossible since BINLOG_FORMAT =
ROW and at least one table uses a storage
engine that is not capable of row-based logging. | - |
| Row Injection | STATEMENT | Yes | No | Error: Cannot execute row injection: Binary logging is not possible since at least one table uses a storage engine that is not capable of row-based logging. | - |
| Row Injection | MIXED | Yes | No | Error: Cannot execute row injection: Binary logging is not possible since at least one table uses a storage engine that is not capable of row-based logging. | - |
| Row Injection | ROW | Yes | No | Error: Cannot execute row injection: Binary logging is not possible since at least one table uses a storage engine that is not capable of row-based logging. | - |
| Safe | STATEMENT | No | Yes | Error: Cannot execute statement: Binary logging
is impossible since BINLOG_FORMAT =
STATEMENT and at least one table uses a
storage engine that is not capable of statement-based
logging. | - |
| Safe | MIXED | No | Yes | - | ROW |
| Safe | ROW | No | Yes | - | ROW |
| Unsafe | STATEMENT | No | Yes | Error: Cannot execute statement: Binary logging
is impossible since BINLOG_FORMAT =
STATEMENT and at least one table uses a
storage engine that is not capable of statement-based
logging. | - |
| Unsafe | MIXED | No | Yes | - | ROW |
| Unsafe | ROW | No | Yes | - | ROW |
| Row Injection | STATEMENT | No | Yes | Error: Cannot execute row injection: Binary
logging is not possible since BINLOG_FORMAT =
STATEMENT. | - |
| Row Injection | MIXED | No | Yes | - | ROW |
| Row Injection | ROW | No | Yes | - | ROW |
| Safe | STATEMENT | Yes | Yes | - | STATEMENT |
| Safe | MIXED | Yes | Yes | - | STATEMENT |
| Safe | ROW | Yes | Yes | - | ROW |
| Unsafe | STATEMENT | Yes | Yes | Warning: Unsafe statement binlogged in statement
format since BINLOG_FORMAT =
STATEMENT. | STATEMENT |
| Unsafe | MIXED | Yes | Yes | - | ROW |
| Unsafe | ROW | Yes | Yes | - | ROW |
| Row Injection | STATEMENT | Yes | Yes | Error: Cannot execute row injection: Binary
logging is not possible because BINLOG_FORMAT =
STATEMENT. | - |
| Row Injection | MIXED | Yes | Yes | - | ROW |
| Row Injection | ROW | Yes | Yes | - | ROW |
When a warning is produced by the determination, a standard
MySQL warning is produced (and is available using
SHOW WARNINGS). The information
is also written to the mysqld error log. Only
one error for each error instance per client connection is
logged to prevent flooding the log. The log message includes the
SQL statement that was attempted.
If a slave server was started with
log_error_verbosity set to
display warnings, the slave prints messages to the error log to
provide information about its status, such as the binary log and
relay log coordinates where it starts its job, when it is
switching to another relay log, when it reconnects after a
disconnect, statements that are unsafe for statement-based
logging, and so forth.
The contents of the grant tables in the mysql
database can be modified directly (for example, with
INSERT or
DELETE) or indirectly (for
example, with GRANT or
CREATE USER). Statements that
affect mysql database tables are written to
the binary log using the following rules:
Data manipulation statements that change data in
mysqldatabase tables directly are logged according to the setting of thebinlog_formatsystem variable. This pertains to statements such asINSERT,UPDATE,DELETE,REPLACE,DO,LOAD DATA INFILE,SELECT, andTRUNCATE TABLE.Statements that change the
mysqldatabase indirectly are logged as statements regardless of the value ofbinlog_format. This pertains to statements such asGRANT,REVOKE,SET PASSWORD,RENAME USER,CREATE(all forms exceptCREATE TABLE ... SELECT),ALTER(all forms), andDROP(all forms).
CREATE TABLE ...
SELECT is a combination of data definition and data
manipulation. The CREATE TABLE
part is logged using statement format and the
SELECT part is logged according
to the value of binlog_format.
The slow query log consists of SQL statements that took more than
long_query_time seconds to
execute and required at least
min_examined_row_limit rows to be
examined. The minimum and default values of
long_query_time are 0 and 10,
respectively. The value can be specified to a resolution of
microseconds. For logging to a file, times are written including
the microseconds part. For logging to tables, only integer times
are written; the microseconds part is ignored.
By default, administrative statements are not logged, nor are
queries that do not use indexes for lookups. This behavior can be
changed using
log_slow_admin_statements and
log_queries_not_using_indexes, as
described later.
The time to acquire the initial locks is not counted as execution time. mysqld writes a statement to the slow query log after it has been executed and after all locks have been released, so log order might differ from execution order.
By default, the slow query log is disabled. To specify the initial
slow query log state explicitly, use
--slow_query_log[={0|1}]. With no
argument or an argument of 1,
--slow_query_log enables the log.
With an argument of 0, this option disables the log. To specify a
log file name, use
--slow_query_log_file=.
To specify the log destination, use
file_name--log-output (as described in
Section 6.4.1, “Selecting General Query and Slow Query Log Output Destinations”).
If you specify no name for the slow query log file, the default
name is
host_name-slow.log
To disable or enable the slow query log or change the log file
name at runtime, use the global
slow_query_log and
slow_query_log_file system
variables. Set slow_query_log to
0 (or OFF) to disable the log or to 1 (or
ON) to enable it. Set
slow_query_log_file to specify
the name of the log file. If a log file already is open, it is
closed and the new file is opened.
When the slow query log is enabled, the server writes output to
any destinations specified by the
--log-output option or
log_output system variable. If
you enable the log, the server opens the log file and writes
startup messages to it. However, further logging of queries to the
file does not occur unless the FILE log
destination is selected. If the destination is
NONE, the server writes no queries even if the
slow query log is enabled. Setting the log file name has no effect
on logging if the log destination value does not contain
FILE.
The server writes less information to the slow query log if you
use the --log-short-format option.
To include slow administrative statements in the statements
written to the slow query log, use the
log_slow_admin_statements system
variable. Administrative statements include
ALTER TABLE,
ANALYZE TABLE,
CHECK TABLE,
CREATE INDEX,
DROP INDEX,
OPTIMIZE TABLE, and
REPAIR TABLE.
To include queries that do not use indexes for row lookups in the
statements written to the slow query log, enable the
log_queries_not_using_indexes
system variable. When such queries are logged, the slow query log
may grow quickly. It is possible to put a rate limit on these
queries by setting the
log_throttle_queries_not_using_indexes
system variable. By default, this variable is 0, which means there
is no limit. Positive values impose a per-minute limit on logging
of queries that do not use indexes. The first such query opens a
60-second window within which the server logs queries up to the
given limit, then suppresses additional queries. If there are
suppressed queries when the window ends, the server logs a summary
that indicates how many there were and the aggregate time spent in
them. The next 60-second window begins when the server logs the
next query that does not use indexes.
The server uses the controlling parameters in the following order to determine whether to write a query to the slow query log:
The query must either not be an administrative statement, or
log_slow_admin_statementsmust be enabled.The query must have taken at least
long_query_timeseconds, orlog_queries_not_using_indexesmust be enabled and the query used no indexes for row lookups.The query must have examined at least
min_examined_row_limitrows.The query must not be suppressed according to the
log_throttle_queries_not_using_indexessetting.
As of MySQL 5.7.2, the
log_timestamps system variable
controls the timestamp time zone of messages written to the slow
query log file (as well as to the general query log file and the
error log). It does not affect the time zone of general query log
and slow query log messages written to log tables, but rows
retrieved from those tables can be converted from the local system
time zone to any desired time zone with
CONVERT_TZ() or by setting the
session time_zone system
variable. Before MySQL 5.7.2, messages use the local system time
zone.
As of MySQL 5.7.2, all log lines contain a timestamp. Previously, for lines falling in the same second, only the first contained a timestamp.
The server does not write queries handled by the query cache to the slow query log, nor queries that would not benefit from the presence of an index because the table has zero rows or one row.
By default, a replication slave does not write replicated queries
to the slow query log. To change this, use the
log_slow_slave_statements system
variable.
Passwords in statements written to the slow query log are rewritten by the server not to occur literally in plain text. See also Section 7.1.2.3, “Passwords and Logging”.
The slow query log can be used to find queries that take a long time to execute and are therefore candidates for optimization. However, examining a long slow query log can become a difficult task. To make this easier, you can process a slow query log file using the mysqldumpslow command to summarize the queries that appear in the log. See Section 5.6.8, “mysqldumpslow — Summarize Slow Query Log Files”.
The DDL log, or metadata log, records metadata operations
generated by data definition statements such as
DROP TABLE and
ALTER TABLE. MySQL uses this log to
recover from crashes occurring in the middle of a metadata
operation. When executing the statement DROP TABLE t1,
t2, we need to ensure that both t1
and t2 are dropped, and that each table drop is
complete. Another example of this type of SQL statement is
ALTER
TABLE t3 DROP PARTITION p2, where we must make certain
that the partition is completely dropped and that its definition
is removed from the list of partitions for table
t3.
A record of metadata operations such as those just described are
written to the file ddl_log.log, in the MySQL
data directory. This is a binary file; it is not intended to be
human-readable, and you should not attempt to modify it in any
way.
ddl_log.log is not created until it is
actually needed for recording metadata statements, so it is
possible for this file not to be present on a MySQL server that is
functioning in a completely normal manner.
There are no user-configurable server options or variables associated with this file.
As described in Section 6.4, “MySQL Server Logs”, MySQL Server can create several different log files to help you see what activity is taking place. However, you must clean up these files regularly to ensure that the logs do not take up too much disk space.
When using MySQL with logging enabled, you may want to back up and remove old log files from time to time and tell MySQL to start logging to new files. See Section 8.2, “Database Backup Methods”.
On a Linux (Red Hat) installation, you can use the
mysql-log-rotate script for this. If you
installed MySQL from an RPM distribution, this script should have
been installed automatically. Be careful with this script if you
are using the binary log for replication. You should not remove
binary logs until you are certain that their contents have been
processed by all slaves.
On other systems, you must install a short script yourself that you start from cron (or its equivalent) for handling log files.
For the binary log, you can set the
expire_logs_days system variable
to expire binary log files automatically after a given number of
days (see Section 6.1.4, “Server System Variables”). If you are
using replication, you should set the variable no lower than the
maximum number of days your slaves might lag behind the master. To
remove binary logs on demand, use the PURGE
BINARY LOGS statement (see
Section 14.4.1.1, “PURGE BINARY LOGS Syntax”).
You can force MySQL to start using new log files by flushing the
logs. Log flushing occurs when you issue a
FLUSH LOGS
statement or execute a mysqladmin flush-logs,
mysqladmin refresh, mysqldump
--flush-logs, or mysqldump
--master-data command. See Section 14.7.6.3, “FLUSH Syntax”,
Section 5.5.2, “mysqladmin — Client for Administering a MySQL Server”, and Section 5.5.4, “mysqldump — A Database Backup Program”. In
addition, the binary log is flushed when its size reaches the
value of the max_binlog_size
system variable.
FLUSH LOGS
supports optional modifiers to enable selective flushing of
individual logs (for example,
FLUSH BINARY
LOGS).
A log-flushing operation does the following:
If general query logging or slow query logging to a log file is enabled, the server closes and reopens the general query log file or slow query log file.
If binary logging is enabled, the server closes the current binary log file and opens a new log file with the next sequence number.
If the server was started with the
--log-erroroption to cause the error log to be written to a file, the server closes and reopens the log file.
The server creates a new binary log file when you flush the logs.
However, it just closes and reopens the general and slow query log
files. To cause new files to be created on Unix, rename the
current log files before flushing them. At flush time, the server
opens new log files with the original names. For example, if the
general and slow query log files are named
mysql.log and
mysql-slow.log, you can use a series of
commands like this:
shell>cdshell>mysql-data-directorymv mysql.log mysql.oldshell>mv mysql-slow.log mysql-slow.oldshell>mysqladmin flush-logs
On Windows, use rename rather than mv.
At this point, you can make a backup of
mysql.old and
mysql-slow.old and then remove them from
disk.
A similar strategy can be used to back up the error log file, if there is one.
You can rename the general query log or slow query log at runtime by disabling the log:
SET GLOBAL general_log = 'OFF'; SET GLOBAL slow_query_log = 'OFF';
With the logs disabled, rename the log files externally; for example, from the command line. Then enable the logs again:
SET GLOBAL general_log = 'ON'; SET GLOBAL slow_query_log = 'ON';
This method works on any platform and does not require a server restart.
MySQL supports a plugin API that enables creation of server
components. Plugins can be loaded at server startup, or loaded and
unloaded at runtime without restarting the server. The components
supported by this interface include, but are not limited to, storage
engines, INFORMATION_SCHEMA tables, full-text
parser plugins, partitioning support, and server extensions.
MySQL distributions include several plugins that implement server extensions:
Plugins for authenticating attempts by clients to connect to MySQL Server. Plugins are available for several authentication protocols. See Section 7.3.8, “Pluggable Authentication”.
A password-validation plugin implements password strength policies and assesses the strength of potential passwords. See Section 7.5.2, “The Password Validation Plugin”.
Semisynchronous replication plugins implement an interface to replication capabilities that permit the master to proceed as long as at least one slave has responded to each transaction. See Section 18.3.9, “Semisynchronous Replication”.
MySQL Enterprise Edition includes a thread pool plugin that manages connection threads to increase server performance by efficiently managing statement execution threads for large numbers of client connections. See Section 6.5.4, “MySQL Enterprise Thread Pool”.
MySQL Enterprise Edition includes an audit plugin for monitoring and logging of connection and query activity. See Section 7.5.4, “MySQL Enterprise Audit”.
MySQL Enterprise Edition includes a firewall plugin that implements an application-level firewall to enable database administrators to permit or deny SQL statement execution based on matching against whitelists of accepted statement patterns. See Section 7.5.5, “MySQL Enterprise Firewall”.
A query rewrite plugin examines statements received by MySQL Server and possibly rewrites them before the server executes them. See Section 6.5.5, “The Rewriter Query Rewrite Plugin”
Version Tokens enables creation of and synchronization around server tokens that applications can use to prevent accessing incorrect or out-of-date data. Version Tokens is based on a plugin library that implements a
version_tokensplugin and a set of user-defined functions. See Section 6.5.6, “Version Tokens”.Keyring plugins provide secure storage for sensitive information. See Section 7.5.3, “The MySQL Keyring”.
X Plugin extends MySQL Server to be able to function as a document store. Running X Plugin enables MySQL Server to communicate with clients using the X Protocol, which is designed to expose the ACID compliant storage abilities of MySQL as a document store. See Section 3.7, “X Plugin”.
Plugins for testing server services. For information about these plugins, see Plugins for Testing Plugin Services, in The MySQL Test Framework, Version 2.0.
The following sections describe how to install and uninstall plugins, and how to determine at runtime which plugins are installed and obtain information about them. For information about writing plugins, see Section 26.2, “The MySQL Plugin API”.
Server plugins must be loaded into the server before they can be used. MySQL supports plugin loading at server startup and runtime. It is also possible to control the activation state of loaded plugins at startup, and to unload them at runtime.
While a plugin is loaded, information about it is available at
runtime from the
INFORMATION_SCHEMA.PLUGINS table and
the SHOW PLUGINS statement. See
Section 6.5.3, “Obtaining Server Plugin Information”.
Before a server plugin can be used, it must be installed using
one of the following methods. In the descriptions,
plugin_name stands for a plugin name
such as innodb, csv, or
validate_password.
Built-in plugins:
A built-in plugin is known by the server automatically.
Normally, the server enables the plugin at startup. Some
built-in plugins permit this to be changed with the
--
option.
plugin_name[=activation_state]
Plugins registered in the
mysql.plugin system table:
The mysql.plugin table serves as a registry
of plugins (other than built-in plugins, which need not be
registered). At startup, the server loads each plugin listed in
the table. Normally, for a plugin loaded from the
mysql.plugin table, the server also enables
the plugin. This can be changed with the
--
option.
plugin_name[=activation_state]
If the server is started with the
--skip-grant-tables option, it
does not consult the mysql.plugin table and
does not load the plugins listed there.
Plugins named with command-line options:
A plugin located in a plugin library file can be loaded at
server startup with the
--plugin-load,
--plugin-load-add, or (as of
MySQL 5.7.11) --early-plugin-load
option. Normally, for a plugin loaded at startup, the server
also enables the plugin. This can be changed with the
--
option.
plugin_name[=activation_state]
The --plugin-load and
--plugin-load-add options load
plugins after built-in plugins and storage engines have
initialized during the server startup sequence. The
--early-plugin-load option is
used to load plugins that must be available prior to
initialization of built-in plugins and storage engines.
The value of each plugin-loading option is a semicolon-separated
list of
name=plugin_library
and plugin_library values. Each
name is the name of a plugin to load,
and plugin_library is the name of the
library file that contains the plugin code. If a plugin library
is named without any preceding plugin name, the server loads all
plugins in the library. The server looks for plugin library
files in the directory named by the
plugin_dir system variable.
Plugin-loading options do not register any plugin in the
mysql.plugin table. For subsequent restarts,
the server loads the plugin again only if
--plugin-load,
--plugin-load-add, or
--early-plugin-load is given
again. That is, the option produces a one-time
plugin-installation operation that persists for a single server
invocation.
--plugin-load,
--plugin-load-add, and
--early-plugin-load enable
plugins to be loaded even when
--skip-grant-tables is given
(which causes the server to ignore the
mysql.plugin table).
--plugin-load,
--plugin-load-add, and
--early-plugin-load also enable
plugins to be loaded at startup that cannot be loaded at
runtime.
The --plugin-load-add option
complements the --plugin-load
option:
--plugin-load-addadds a plugin or plugins to the set of plugins to be loaded at startup.The argument format is the same as for
--plugin-load, but--plugin-load-addcan be used to avoid specifying a large set of plugins as a single long unwieldy--plugin-loadargument.--plugin-load-addcan be given in the absence of--plugin-load, but any instance of--plugin-load-addthat appears before--plugin-loadhas no effect because--plugin-loadresets the set of plugins to load.
For example, these options:
--plugin-load=x --plugin-load-add=y
are equivalent to this option:
--plugin-load="x;y"
But these options:
--plugin-load-add=y --plugin-load=x
are equivalent to this option:
--plugin-load=x
Plugins installed with the
INSTALL PLUGIN
statement:
A plugin located in a plugin library file can be loaded at
runtime with the INSTALL PLUGIN
statement. The statement also registers the plugin in the
mysql.plugin table to cause the server to
load it on subsequent restarts. For this reason,
INSTALL PLUGIN requires the
INSERT privilege for the
mysql.plugin table.
The plugin library file base name depends on your platform.
Common suffixes are .so for Unix and
Unix-like systems, .dll for Windows.
Example: The --plugin-load option
installs a plugin at server startup. To install a plugin named
myplugin from a plugin library file named
somepluglib.so, use these lines in a
my.cnf file:
[mysqld] plugin-load=myplugin=somepluglib.so
In this case, the plugin is not registered in
mysql.plugin. Restarting the server without
the --plugin-load option causes
the plugin not to be loaded at startup.
Alternatively, the INSTALL PLUGIN
statement causes the server to load the plugin code from the
library file at runtime:
INSTALL PLUGIN myplugin SONAME 'somepluglib.so';
INSTALL PLUGIN also causes
“permanent” plugin registration: The plugin is
listed in the mysql.plugin table to ensure
that the server loads it on subsequent restarts.
Many plugins can be loaded either at server startup or at
runtime. However, if a plugin is designed such that it must be
loaded and initialized during server startup, attempts to load
it at runtime using INSTALL
PLUGIN produce an error:
mysql> INSTALL PLUGIN myplugin SONAME 'somepluglib.so';
ERROR 1721 (HY000): Plugin 'myplugin' is marked as not dynamically
installable. You have to stop the server to install it.
In this case, you must use
--plugin-load,
--plugin-load-add, or
--early-plugin-load.
If a plugin is named both using a
--plugin-load,
--plugin-load-add, or
--early-plugin-load option and
(as a result of an earlier INSTALL
PLUGIN statement) in the
mysql.plugin table, the server starts but
writes these messages to the error log:
[ERROR] Function 'plugin_name' already exists [Warning] Couldn't load plugin named 'plugin_name' with soname 'plugin_object_file'.
If the server knows about a plugin when it starts (for example,
because the plugin is named using a
--plugin-load option or is
registered in the mysql.plugin table), the
server loads and enables the plugin by default. It is possible
to control activation state for such a plugin using a
--
startup option, where plugin_name[=activation_state]plugin_name is
the name of the plugin to affect, such as
innodb, csv, or
validate_password. As with other options,
dashes and underscores are interchangeable in option names.
Also, activation state values are not case sensitive. For
example, --my_plugin=ON and
--my-plugin=on are equivalent.
--plugin_name=OFFTells the server to disable the plugin. This may not be possible for certain built-in plugins, such as
mysql_native_password.--plugin_name[=ON]Tells the server to enable the plugin. (Specifying the option as
--without a value has the same effect.) If the plugin fails to initialize, the server runs with the plugin disabled.plugin_name--plugin_name=FORCETells the server to enable the plugin, but if plugin initialization fails, the server does not start. In other words, this option forces the server to run with the plugin enabled or not at all.
--plugin_name=FORCE_PLUS_PERMANENTLike
FORCE, but in addition prevents the plugin from being unloaded at runtime. If a user attempts to do so withUNINSTALL PLUGIN, an error occurs.
Plugin activation states are visible in the
LOAD_OPTION column of the
INFORMATION_SCHEMA.PLUGINS table.
Suppose that CSV,
BLACKHOLE, and ARCHIVE are
built-in pluggable storage engines and that you want the server
to load them at startup, subject to these conditions: The server
is permitted to run if CSV initialization
fails, must require that BLACKHOLE
initialization succeeds, and should disable
ARCHIVE. To accomplish that, use these lines
in an option file:
[mysqld] csv=ON blackhole=FORCE archive=OFF
The
--enable-
option format is a synonym for
plugin_name--.
The
plugin_name=ON--disable-
and
plugin_name--skip-
option formats are synonyms for
plugin_name--.
plugin_name=OFF
If a plugin is disabled, either explicitly with
OFF or implicitly because it was enabled with
ON but failed to initialize, aspects of
server operation that require the plugin will change. For
example, if the plugin implements a storage engine, existing
tables for the storage engine become inaccessible, and attempts
to create new tables for the storage engine result in tables
that use the default storage engine unless the
NO_ENGINE_SUBSTITUTION SQL
mode is enabled to cause an error to occur instead.
Disabling a plugin may require adjustment to other options. For
example, if you start the server using
--skip-innodb
to disable InnoDB, other
innodb_
options likely will need to be omitted at startup. In addition,
because xxxInnoDB is the default
storage engine, it will not start unless you specify another
available storage engine with
--default_storage_engine. You
must also set
--default_tmp_storage_engine.
At runtime, the UNINSTALL PLUGIN
statement disables and uninstalls a plugin known to the server.
The statement unloads the plugin and removes it from the
mysql.plugin table, if it is registered
there. For this reason, UNINSTALL
PLUGIN statement requires the
DELETE privilege for the
mysql.plugin table. With the plugin no longer
registered in the table, the server will not load the plugin
automatically for subsequent restarts.
UNINSTALL PLUGIN can unload a
plugin regardless of whether it was loaded at runtime with
INSTALL PLUGIN or at startup with
a plugin-loading option, subject to these conditions:
It cannot unload plugins that are built in to the server. These can be identified as those that have a library name of
NULLin the output fromINFORMATION_SCHEMA.PLUGINSorSHOW PLUGINS.It cannot unload plugins for which the server was started with
--, which prevents plugin unloading at runtime. These can be identified from theplugin_name=FORCE_PLUS_PERMANENTLOAD_OPTIONcolumn of theINFORMATION_SCHEMA.PLUGINStable.
To uninstall a plugin that currently is loaded at server startup with a plugin-loading option, use this procedure.
Remove any options related to the plugin from the
my.cnffile.Restart the server.
Plugins normally are installed using either a plugin-loading option at startup or with
INSTALL PLUGINat runtime, but not both. However, removing options for a plugin from themy.cnffile may not be sufficient to uninstall it if at some pointINSTALL PLUGINhas also been used. If the plugin still appears in the output fromINFORMATION_SCHEMA.PLUGINSorSHOW PLUGINS, useUNINSTALL PLUGINto remove it from themysql.plugintable. Then restart the server again.
There are several ways to determine which plugins are installed in the server:
The
INFORMATION_SCHEMA.PLUGINStable contains a row for each loaded plugin. Any that have aPLUGIN_LIBRARYvalue ofNULLare built in and cannot be unloaded.mysql>
SELECT * FROM information_schema.PLUGINS\G*************************** 1. row *************************** PLUGIN_NAME: binlog PLUGIN_VERSION: 1.0 PLUGIN_STATUS: ACTIVE PLUGIN_TYPE: STORAGE ENGINE PLUGIN_TYPE_VERSION: 50158.0 PLUGIN_LIBRARY: NULL PLUGIN_LIBRARY_VERSION: NULL PLUGIN_AUTHOR: MySQL AB PLUGIN_DESCRIPTION: This is a pseudo storage engine to represent the binlog in a transaction PLUGIN_LICENSE: GPL LOAD_OPTION: FORCE ... *************************** 10. row *************************** PLUGIN_NAME: InnoDB PLUGIN_VERSION: 1.0 PLUGIN_STATUS: ACTIVE PLUGIN_TYPE: STORAGE ENGINE PLUGIN_TYPE_VERSION: 50158.0 PLUGIN_LIBRARY: ha_innodb_plugin.so PLUGIN_LIBRARY_VERSION: 1.0 PLUGIN_AUTHOR: Innobase Oy PLUGIN_DESCRIPTION: Supports transactions, row-level locking, and foreign keys PLUGIN_LICENSE: GPL LOAD_OPTION: ON ...The
SHOW PLUGINSstatement displays a row for each loaded plugin. Any that have aLibraryvalue ofNULLare built in and cannot be unloaded.mysql>
SHOW PLUGINS\G*************************** 1. row *************************** Name: binlog Status: ACTIVE Type: STORAGE ENGINE Library: NULL License: GPL ... *************************** 10. row *************************** Name: InnoDB Status: ACTIVE Type: STORAGE ENGINE Library: ha_innodb_plugin.so License: GPL ...The
mysql.plugintable shows which plugins have been registered withINSTALL PLUGIN. The table contains only plugin names and library file names, so it does not provide as much information as thePLUGINStable or theSHOW PLUGINSstatement.
MySQL Enterprise Thread Pool is an extension included in MySQL Enterprise Edition, a commercial product. To learn more about commercial products, http://www.mysql.com/products/.
As of MySQL 5.7.9, MySQL Enterprise Edition includes MySQL Enterprise Thread Pool, implemented using a server plugin. The default thread-handling model in MySQL Server executes statements using one thread per client connection. As more clients connect to the server and execute statements, overall performance degrades. The thread pool plugin provides an alternative thread-handling model designed to reduce overhead and improve performance. The plugin implements a thread pool that increases server performance by efficiently managing statement execution threads for large numbers of client connections.
The thread pool addresses several problems of the one thread per connection model:
Too many thread stacks make CPU caches almost useless in highly parallel execution workloads. The thread pool promotes thread stack reuse to minimize the CPU cache footprint.
With too many threads executing in parallel, context switching overhead is high. This also presents a challenging task to the operating system scheduler. The thread pool controls the number of active threads to keep the parallelism within the MySQL server at a level that it can handle and that is appropriate for the server host on which MySQL is executing.
Too many transactions executing in parallel increases resource contention. In
InnoDB, this increases the time spent holding central mutexes. The thread pool controls when transactions start to ensure that not too many execute in parallel.
The thread pool plugin is included only in MySQL Enterprise Edition. It is not included in MySQL community distributions.
On Windows, the thread pool plugin requires Windows Vista or newer. On Linux, the plugin requires kernel 2.6.9 or higher.
Additional Resources
Section A.14, “MySQL 5.7 FAQ: MySQL Enterprise Thread Pool”
The thread pool feature comprises these components:
A plugin library file contains a plugin for the thread pool code and plugins for several
INFORMATION_SCHEMAtables.For a detailed description of how the thread pool works, see Section 6.5.4.3, “Thread Pool Operation”.
The
INFORMATION_SCHEMAtables are namedTP_THREAD_STATE,TP_THREAD_GROUP_STATE, andTP_THREAD_GROUP_STATS. These tables provide information about thread pool operation. For more information, see Section 22.32, “Thread Pool INFORMATION_SCHEMA Tables”.Several system variables are related to the thread pool. The
thread_handlingsystem variable has a value ofloaded-dynamicallywhen the server successfully loads the thread pool plugin.The other related variables are implemented by the thread pool plugin; they are not available unless it is enabled:
thread_pool_algorithm: The concurrency algorithm to use for scheduling.thread_pool_high_priority_connection: How to schedule statement execution for a session.thread_pool_prio_kickup_timer: How long before the thread pool moves a statement awaiting execution from the low-priority queue to the high-priority queue.thread_pool_max_unused_threads: How many sleeping threads to permit.thread_pool_size: The number of thread groups in the thread pool. This is the most important parameter controlling thread pool performance.thread_pool_stall_limit: The time before an executing statement is considered to be stalled.
If any variable implemented by the plugin is set to an illegal value at startup, plugin initialization fails and the plugin does not load.
For information about setting thread pool parameters, see Section 6.5.4.4, “Thread Pool Tuning”.
The Performance Schema exposes information about the thread pool and may be used to investigate operational performance. For more information, see Chapter 23, MySQL Performance Schema.
This section describes how to install MySQL Enterprise Thread Pool. For general information about installing plugins, see Section 6.5.2, “Installing and Uninstalling Plugins”.
To be usable by the server, the plugin library file must be
located in the MySQL plugin directory (the directory named by
the plugin_dir system
variable). If necessary, set the value of
plugin_dir at server startup to
tell the server the plugin directory location.
The plugin library file base name is
thread_pool. The file name suffix differs per
platform (for example, .so for Unix and
Unix-like systems, .dll for Windows).
To enable thread pool capability, load the plugins to be used by
starting the server with the
--plugin-load option. For
example, if you name just the plugin library file, the server
loads all plugins that it contains (that is, the thread pool
plugin and all the INFORMATION_SCHEMA
tables). To do this, put these lines in your
my.cnf file (adjust the
.so suffix for your platform as necessary):
[mysqld] plugin-load=thread_pool.so
That is equivalent to loading all thread pool plugins by naming them individually:
[mysqld] plugin-load=thread_pool=thread_pool.so;tp_thread_state=thread_pool.so;tp_thread_group_state=thread_pool.so;tp_thread_group_stats=thread_pool.so
With --plugin-load, all plugins
must be named on a single line. To make the option file easier
to read, use --plugin-load-add,
which enables naming plugins individually:
[mysqld] plugin-load-add=thread_pool=thread_pool.so plugin-load-add=tp_thread_state=thread_pool.so plugin-load-add=tp_thread_group_state=thread_pool.so plugin-load-add=tp_thread_group_stats=thread_pool.so
If desired, you can load individual plugins from the library
file. To load the thread pool plugin but not the
INFORMATION_SCHEMA tables, use an option like
this:
[mysqld] plugin-load=thread_pool=thread_pool.so
To load the thread pool plugin and only the
TP_THREAD_STATE
INFORMATION_SCHEMA table, use an option like
this:
[mysqld] plugin-load=thread_pool=thread_pool.so;tp_thread_state=thread_pool.so
If you do not load all the
INFORMATION_SCHEMA tables, some or all
MySQL Enterprise Monitor thread pool graphs will be empty.
To verify plugin installation, examine the
INFORMATION_SCHEMA.PLUGINS table or
use the SHOW PLUGINS statement
(see Section 6.5.3, “Obtaining Server Plugin Information”). For
example:
mysql>SELECT PLUGIN_NAME, PLUGIN_STATUS FROM INFORMATION_SCHEMA.PLUGINS->WHERE PLUGIN_NAME LIKE 'thread%' OR PLUGIN_NAME LIKE 'tp%';+-----------------------+---------------+ | PLUGIN_NAME | PLUGIN_STATUS | +-----------------------+---------------+ | thread_pool | ACTIVE | | TP_THREAD_STATE | ACTIVE | | TP_THREAD_GROUP_STATE | ACTIVE | | TP_THREAD_GROUP_STATS | ACTIVE | +-----------------------+---------------+
If the server loads the thread pool plugin successfully, it sets
the thread_handling system variable to
dynamically-loaded. If the plugin fails to
load, the server writes a message to the error log.
The thread pool consists of a number of thread groups, each of which manages a set of client connections. As connections are established, the thread pool assigns them to thread groups in round-robin fashion.
The number of thread groups is configurable using the
thread_pool_size system
variable. The default number of groups is 16. For guidelines on
setting this variable, see Section 6.5.4.4, “Thread Pool Tuning”.
The maximum number of threads per group is 4096 (or 4095 on some systems where one thread is used internally).
The thread pool separates connections and threads, so there is no fixed relationship between connections and the threads that execute statements received from those connections. This differs from the default thread-handling model that associates one thread with one connection such that the thread executes all statements from the connection.
The thread pool tries to ensure a maximum of one thread executing in each group at any time, but sometimes permits more threads to execute temporarily for best performance. The algorithm works in the following manner:
Each thread group has a listener thread that listens for incoming statements from the connections assigned to the group. When a statement arrives, the thread group either begins executing it immediately or queues it for later execution:
Immediate execution occurs if the statement is the only one received and no statements are queued or currently executing.
Queuing occurs if the statement cannot begin executing immediately.
If immediate execution occurs, execution is performed by the listener thread. (This means that temporarily no thread in the group is listening.) If the statement finishes quickly, the executing thread returns to listening for statements. Otherwise, the thread pool considers the statement stalled and starts another thread as a listener thread (creating it if necessary). To ensure that no thread group becomes blocked by stalled statements, the thread pool has a background thread that regularly monitors thread group states.
By using the listening thread to execute a statement that can begin immediately, there is no need to create an additional thread if the statement finishes quickly. This ensures the most efficient execution possible in the case of a low number of concurrent threads.
When the thread pool plugin starts, it creates one thread per group (the listener thread), plus the background thread. Additional threads are created as necessary to execute statements.
The value of the
thread_pool_stall_limitsystem variable determines the meaning of “finishes quickly” in the previous item. The default time before threads are considered stalled is 60ms but can be set to a maximum of 6s. This parameter is configurable to enable you to strike a balance appropriate for the server work load. Short wait values permit threads to start more quickly. Short values are also better for avoiding deadlock situations. Long wait values are useful for workloads that include long-running statements, to avoid starting too many new statements while the current ones execute.The thread pool focuses on limiting the number of concurrent short-running statements. Before an executing statement reaches the stall time, it prevents other statements from beginning to execute. If the statement executes past the stall time, it is permitted to continue but no longer prevents other statements from starting. In this way, the thread pool tries to ensure that in each thread group there is never more than one short-running statement, although there might be multiple long-running statements. It is undesirable to let long-running statements prevent other statements from executing because there is no limit on the amount of waiting that might be necessary. For example, on a replication master, a thread that is sending binary log events to a slave effectively runs forever.
A statement becomes blocked if it encounters a disk I/O operation or a user level lock (row lock or table lock). The block would cause the thread group to become unused, so there are callbacks to the thread pool to ensure that the thread pool can immediately start a new thread in this group to execute another statement. When a blocked thread returns, the thread pool permits it to restart immediately.
There are two queues, a high-priority queue and a low-priority queue. The first statement in a transaction goes to the low-priority queue. Any following statements for the transaction go to the high-priority queue if the transaction is ongoing (statements for it have begun executing), or to the low-priority queue otherwise. Queue assignment can be affected by enabling the
thread_pool_high_priority_connectionsystem variable, which causes all queued statements for a session to go into the high-priority queue.Statements for a nontransactional storage engine, or a transactional engine if
autocommitis enabled, are treated as low-priority statements because in this case each statement is a transaction. Thus, given a mix of statements forInnoDBandMyISAMtables, the thread pool prioritizes those forInnoDBover those forMyISAMunlessautocommitis enabled. Withautocommitenabled, all statements will be low priority.When the thread group selects a queued statement for execution, it first looks in the high-priority queue, then in the low-priority queue. If a statement is found, it is removed from its queue and begins to execute.
If a statement stays in the low-priority queue too long, the thread pool moves to the high-priority queue. The value of the
thread_pool_prio_kickup_timersystem variable controls the time before movement. For each thread group, a maximum of one statement per 10ms or 100 per second will be moved from the low-priority queue to the high-priority queue.The thread pool reuses the most active threads to obtain a much better use of CPU caches. This is a small adjustment that has a great impact on performance.
While a thread executes a statement from a user connection, Performance Schema instrumentation accounts thread activity to the user connection. Otherwise, Performance Schema accounts activity to the thread pool.
Here are examples of conditions under which a thread group might have multiple threads started to execute statements:
One thread begins executing a statement, but runs long enough to be considered stalled. The thread group permits another thread to begin executing another statement even through the first thread is still executing.
One thread begins executing a statement, then becomes blocked and reports this back to the thread pool. The thread group permits another thread to begin executing another statement.
One thread begins executing a statement, becomes blocked, but does not report back that it is blocked because the block does not occur in code that has been instrumented with thread pool callbacks. In this case, the thread appears to the thread group to be still running. If the block lasts long enough for the statement to be considered stalled, the group permits another thread to begin executing another statement.
The thread pool is designed to be scalable across an increasing number of connections. It is also designed to avoid deadlocks that can arise from limiting the number of actively executing statements. It is important that threads that do not report back to the thread pool do not prevent other statements from executing and thus cause the thread pool to become deadlocked. Examples of such statements follow:
Long-running statements. These would lead to all resources used by only a few statements and they could prevent all others from accessing the server.
Binary log dump threads that read the binary log and send it to slaves. This is a kind of long-running “statement” that runs for a very long time, and that should not prevent other statements from executing.
Statements blocked on a row lock, table lock, sleep, or any other blocking activity that has not been reported back to the thread pool by MySQL Server or a storage engine.
In each case, to prevent deadlock, the statement is moved to the stalled category when it does not complete quickly, so that the thread group can permit another statement to begin executing. With this design, when a thread executes or becomes blocked for an extended time, the thread pool moves the thread to the stalled category and for the rest of the statement's execution, it does not prevent other statements from executing.
The maximum number of threads that can occur is the sum of
max_connections and
thread_pool_size. This can
happen in a situation where all connections are in execution
mode and an extra thread is created per group to listen for more
statements. This is not necessarily a state that happens often,
but it is theoretically possible.
This section provides guidelines on setting thread pool system variables for best performance, measured using a metric such as transactions per second.
thread_pool_size is the most
important parameter controlling thread pool performance. It can
be set only at server startup. Our experience in testing the
thread pool indicates the following:
If the primary storage engine is
InnoDB, the optimalthread_pool_sizesetting is likely to be between 16 and 36, with the most common optimal values tending to be from 24 to 36. We have not seen any situation where the setting has been optimal beyond 36. There may be special cases where a value smaller than 16 is optimal.For workloads such as DBT2 and Sysbench, the optimum for
InnoDBseems to be usually around 36. For very write-intensive workloads, the optimal setting can sometimes be lower.If the primary storage engine is
MyISAM, thethread_pool_sizesetting should be fairly low. We tend to get optimal performance for values from 4 to 8. Higher values tend to have a slightly negative but not dramatic impact on performance.
Another system variable,
thread_pool_stall_limit, is
important for handling of blocked and long-running statements.
If all calls that block the MySQL Server are reported to the
thread pool, it would always know when execution threads are
blocked. However, this may not always be true. For example,
blocks could occur in code that has not been instrumented with
thread pool callbacks. For such cases, the thread pool must be
able to identify threads that appear to be blocked. This is done
by means of a timeout, the length of which can be tuned using
the thread_pool_stall_limit
system variable. This parameter ensures that the server does not
become completely blocked. The value of
thread_pool_stall_limit has an
upper limit of 6 seconds to prevent the risk of a deadlocked
server.
thread_pool_stall_limit also
enables the thread pool to handle long-running statements. If a
long-running statement was permitted to block a thread group,
all other connections assigned to the group would be blocked and
unable to start execution until the long-running statement
completed. In the worst case, this could take hours or even
days.
The value of
thread_pool_stall_limit should
be chosen such that statements that execute longer than its
value are considered stalled. Stalled statements generate a lot
of extra overhead since they involve extra context switches and
in some cases even extra thread creations. On the other hand,
setting the
thread_pool_stall_limit
parameter too high means that long-running statements will block
a number of short-running statements for longer than necessary.
Short wait values permit threads to start more quickly. Short
values are also better for avoiding deadlock situations. Long
wait values are useful for workloads that include long-running
statements, to avoid starting too many new statements while the
current ones execute.
Suppose a server executes a workload where 99.9% of the
statements complete within 100ms even when the server is loaded,
and the remaining statements take between 100ms and 2 hours
fairly evenly spread. In this case, it would make sense to set
thread_pool_stall_limit to 10
(meaning 100ms). The default value of 60ms is okay for servers
that primarily execute very simple statements.
The thread_pool_stall_limit
parameter can be changed at runtime to enable you to strike a
balance appropriate for the server work load. Assuming that the
TP_THREAD_GROUP_STATS table is enabled, you
can use the following query to determine the fraction of
executed statements that stalled:
SELECT SUM(STALLED_QUERIES_EXECUTED) / SUM(QUERIES_EXECUTED) FROM information_schema.TP_THREAD_GROUP_STATS;
This number should be as low as possible. To decrease the
likelihood of statements stalling, increase the value of
thread_pool_stall_limit.
When a statement arrives, what is the maximum time it can be delayed before it actually starts executing? Suppose that the following conditions apply:
There are 200 statements queued in the low-priority queue.
There are 10 statements queued in the high-priority queue.
thread_pool_prio_kickup_timeris set to 10000 (10 seconds).thread_pool_stall_limitis set to 100 (1 second).
In the worst case, the 10 high-priority statements represent 10 transactions that continue executing for a long time. Thus, in the worst case, no statements will be moved to the high-priority queue because it will always already contain statements awaiting execution. After 10 seconds, the new statement is eligible to be moved to the high-priority queue. However, before it can be moved, all the statements before it must be moved as well. This could take another 2 seconds because a maximum of 100 statements per second are moved to the high-priority queue. Now when the statement reaches the high-priority queue, there could potentially be many long-running statements ahead of it. In the worst case, every one of those will become stalled and it will take 1 second for each statement before the next statement is retrieved from the high-priority queue. Thus, in this scenario, it will take 222 seconds before the new statement starts executing.
This example shows a worst case for an application. How to handle it depends on the application. If the application has high requirements for the response time, it should most likely throttle users at a higher level itself. Otherwise, it can use the thread pool configuration parameters to set some kind of a maximum waiting time.
As of MySQL 5.7.6, MySQL Server supports query rewrite plugins that can examine and possibly modify statements received by the server before the server executes them. See Query Rewrite Plugins.
MySQL distributions include a postparse query rewrite plugin named
Rewriter and scripts for installing the plugin
and its associated components. These components work together to
provide SELECT rewriting
capability:
A server-side plugin named
RewriterexaminesSELECTstatements and may rewrite them, based on its in-memory cache of rewrite rules. StandaloneSELECTstatements andSELECTstatements in prepared statements are subject to rewriting.SELECTstatements occurring within view definitions or stored programs are not subject to rewriting.The
Rewriterplugin uses a database namedquery_rewritecontaining a table namedrewrite_rules. The table provides persistent storage for the rules that the plugin uses to decide whether to rewrite statements. Users communicate with the plugin by modifying the set of rules stored in this table. The plugin communicates with users by setting themessagecolumn of table rows.The
query_rewritedatabase contains a stored procedure namedflush_rewrite_rules()that loads the contents of the rules table into the plugin.A user-defined function named
load_rewrite_rules()is used by theflush_rewrite_rules()stored procedure.The
Rewriterplugin exposes system variables that enable plugin configuration and status variables that provide runtime operational information.
The following sections describe how to install and use the
Rewriter plugin, and provide reference
information for its associated components.
If installed, the Rewriter plugin involves
some overhead even when disabled. To avoid this overhead, do
not install the plugin unless you plan to use it.
To install or uninstall the Rewriter query
rewrite plugin, choose the approropriate script located in the
share directory of your MySQL installation:
install_rewriter.sql: Choose this script to install theRewriterplugin and its associated components.NoteBefore MySQL 5.7.8, there are two installation scripts,
install_rewriter.sqlandinstall_rewriter_with_optional_columns.sql, which differ in whether they create thepattern_digestandnormalized_columnscolumns of therewrite_rulestable. As of 5.7.8, the installation script always creates these columns. (For details about the table columns, see Section 6.5.5.3.1, “Rewriter Query Rewrite Plugin Rules Table”.)uninstall_rewriter.sql: Choose this script to uninstall theRewriterplugin and its associated components.
Run the chosen script as follows:
shell>mysql -u root -p < install_rewriter.sqlEnter password:(enter root password here)
The example here uses the
install_rewriter.sql installation script.
Make the appropriate substitution if you choose a different
script.
Running an installation script should install and enable the plugin. To verify that, connect to the server and execute this statement:
mysql> SHOW GLOBAL VARIABLES LIKE 'rewriter_enabled';
+------------------+-------+
| Variable_name | Value |
+------------------+-------+
| rewriter_enabled | ON |
+------------------+-------+
For usage instructions, see Section 6.5.5.2, “Using the Rewriter Query Rewrite Plugin”. For reference information, see Section 6.5.5.3, “Rewriter Query Rewrite Plugin Reference”.
To enable or disable the plugin, enable or disable the
rewriter_enabled system
variable. By default, the Rewriter plugin is
enabled when you install it (see
Section 6.5.5.1, “Installing or uninstalling the Rewriter Query Rewrite Plugin”).
To set the initial plugin state explicitly, you can set the
variable at server startup. For example, to enable the plugin in
an option file, use these lines:
[mysqld] rewriter_enabled=ON
It is also possible to enable or disable the plugin at runtime:
mosql>SET GLOBAL rewriter_enabled = ON;mysql>SET GLOBAL rewriter_enabled = OFF;
Asumming that the Rewriter plugin is enabled,
it examines and possibly modifies each
SELECT statement received by the
server. The plugin determines whether to rewrite statements
based on its in-memory cache of rewriting rules, which are
loaded from the rewrite_rules table in the
query_rewrite database.
Adding Rewrite Rules
To add rules for the Rewriter plugin, add
rows to the rewrite_rules table, then invoke
the flush_rewrite_rules() stored procedure to
load the rules from the table into the plugin. The following
example creates a simple rule to match statements that select a
single literal value:
mysql>INSERT INTO query_rewrite.rewrite_rules (pattern, replacement)->VALUES('SELECT ?', 'SELECT ? + 1');
The resulting table contents look like this:
mysql> SELECT * FROM query_rewrite.rewrite_rules\G
*************************** 1. row ***************************
id: 1
pattern: SELECT ?
pattern_database: NULL
replacement: SELECT ? + 1
enabled: YES
message: NULL
pattern_digest: NULL
normalized_pattern: NULL
The rule specifies a pattern template indicating which
SELECT statements to match, and a
replacement template indicating how to rewrite matching
statements. However, adding the rule to the
rewrite_rules table is not sufficient to
cause the Rewriter plugin to use the rule.
You must invoke flush_rewrite_rules() to load
the table contents into the plugin in-memory cache:
mysql> CALL query_rewrite.flush_rewrite_rules();
If your rewrite rules seem not to be working properly, make
sure that you have reloaded the rules table by calling
flush_rewrite_rules().
When the plugin reads each rule from the rules table, it
computes a normalized form (digest) from the pattern and a
digest hash value, and updates the
normalized_pattern and
pattern_digest columns:
mysql> SELECT * FROM query_rewrite.rewrite_rules\G
*************************** 1. row ***************************
id: 1
pattern: SELECT ?
pattern_database: NULL
replacement: SELECT ? + 1
enabled: YES
message: NULL
pattern_digest: 46b876e64cd5c41009d91c754921f1d4
normalized_pattern: select ?
For information about statement digesting and normalized statements, see Section 23.7, “Performance Schema Statement Digests”.
Patterns use the same syntax as prepared statements (see
Section 14.5.1, “PREPARE Syntax”). Within a pattern template,
? characters act as parameter markers that
match data values. Parameter markers can be used only where data
values should appear, not for SQL keywords, identifiers, and so
forth. The ? characters should not be
enclosed within quotation marks.
Like the pattern, the replacement can contain
? characters. For a statement that matches a
pattern template, the plugin rewrites it, replacing
? parameter markers in the replacement using
data values matched by the corresponding markers in the pattern.
The result is a complete statement string. The plugin asks the
server to parse it, and returns the result to the server as the
representation of the rewritten statement.
After adding and loading the rule, check whether rewriting occurs according to whether statements match the rule pattern:
mysql>SELECT PI();+----------+ | PI() | +----------+ | 3.141593 | +----------+ 1 row in set (0.01 sec) mysql>SELECT 10;+--------+ | 10 + 1 | +--------+ | 11 | +--------+ 1 row in set, 1 warning (0.00 sec)
No rewriting occurs for the first
SELECT statment, but does for the
second. The second statement illustrates that when the
Rewriter plugin rewrites a statement, it
produces a warning message. To view the message, use
SHOW WARNINGS:
mysql> SHOW WARNINGS\G
*************************** 1. row ***************************
Level: Note
Code: 1105
Message: Query 'SELECT 10' rewritten to 'SELECT 10 + 1' by a query rewrite plugin
To enable or disable an existing rule, modify its
enabled column and reload the table into the
plugin. To disable rule 1:
mysql>UPDATE query_rewrite.rewrite_rules SET enabled = 'NO' WHERE id = 1;mysql>CALL query_rewrite.flush_rewrite_rules();
This enables you to deactivate a rule without removing it from the table.
To re-enable rule 1:
mysql>UPDATE query_rewrite.rewrite_rules SET enabled = 'YES' WHERE id = 1;mysql>CALL query_rewrite.flush_rewrite_rules();
The rewrite_rules table contains a
pattern_database column that
Rewriter uses for matching table names that
are not qualified with a database name:
Qualified table names in statements match qualified names in the pattern if corresponding database and table names are identical.
Unqualified table names in statements match unqualified names in the pattern only if the default database is the same as
pattern_databaseand the table names are identical.
Suppose that a table named appdb.users has a
column named id and that applications are
expected to select rows from the table using a query of one of
these forms, where the second can be used only if
appdb is the default database:
SELECT * FROM users WHERE appdb.id =id_value; SELECT * FROM users WHERE id =id_value;
Suppose also that the id column is renamed to
user_id (perhaps the table must be modified
to add another type of ID and it is necessary to indicate more
specifically what type of ID the id column
represents).
The change means that applications must refer to
user_id rather than id in
the WHERE clause. But if there are old
applications that cannot be written to change the
SELECT queries they generate, they will no
longer work properly. The Rewriter plugin can
solve this problem. To match and rewrite statements whether or
not they qualify the table name, add the following two rules and
reload the rules table:
mysql>INSERT INTO query_rewrite.rewrite_rules->(pattern, replacement) VALUES(->'SELECT * FROM appdb.users WHERE id = ?',->'SELECT * FROM appdb.users WHERE user_id = ?'->);mysql>INSERT INTO query_rewrite.rewrite_rules->(pattern, replacement, pattern_database) VALUES(->'SELECT * FROM users WHERE id = ?',->'SELECT * FROM users WHERE user_id = ?',->'appdb'->);mysql>CALL query_rewrite.flush_rewrite_rules();
Rewriter uses the first rule to match
statements that use the qualified table name. It uses the second
to match statements that used the unqualified name, but only if
the default database is appdb (the value in
pattern_database).
How Statement Matching Works
The Rewriter plugin uses statement digests to
match incoming statements against rewrite rules in stages. The
max_digest_length system variable determines
the size of the buffer used for computing statement digests.
Larger values enable computation of digests that distinguish
longer statements. Smaller values use less memory but increase
the likelihood of longer statements colliding with the same
digest value.
The plugin matches each statement to the rewrite rules as follows:
Compute the statement digest hash value and compare it to the rule digest hash values. This is subject to false positives, but serves as a quick rejection test.
If the statement digest hash value matches any pattern digest hash values, match the normalized form of the statement to the normalized form of the matching rule patterns.
If the normalized statement matches a rule, compare the literal values in the statement and the pattern. A
?in the pattern matches any literal value in the statement. If the statement prepares aSELECTstatement,?in the pattern also matches?in the statement. Otherwise, corresponding literals must be the same.
If multiple rules match a statement, it is indeterminate which one the plugin uses to rewrite the statement.
If a pattern contains more markers than the replacement, the
plugin discards excess data values. If a pattern contains fewer
markers than the replacement, it is an error. The plugin notices
this when the rules table is loaded, writes an error message to
the message column of the rule row to
communicate the problem, and sets the
Rewriter_reload_error status
variable to ON.
Rewriting Prepared Statements
Prepared statements are rewritten at parse time (that is, when they are prepared), not when they are executed later.
Prepared statements differ from nonprepared statements in that
they may contain ? characters as parameter
markers. To match a ? in a prepared
statement, a Rewriter pattern must contain
? in the same location. Suppose that a
rewrite rule has this pattern:
SELECT ?, 3
The following table shows several prepared
SELECT statements and whether the
rule pattern matches them.
| Prepared Statement | Whether Pattern Matches Statement |
|---|---|
PREPARE s AS 'SELECT 3, 3' | Yes |
PREPARE s AS 'SELECT ?, 3' | Yes |
PREPARE s AS 'SELECT 3, ?' | No |
PREPARE s AS 'SELECT ?, ?' | No |
Rewriter Plugin Operational Information
The Rewriter plugin makes information
available about its operation by means of several status
variables:
mysql> SHOW GLOBAL STATUS LIKE 'Rewriter%';
+-----------------------------------+-------+
| Variable_name | Value |
+-----------------------------------+-------+
| Rewriter_number_loaded_rules | 1 |
| Rewriter_number_reloads | 5 |
| Rewriter_number_rewritten_queries | 1 |
| Rewriter_reload_error | ON |
+-----------------------------------+-------+
For descriptions of these variables, see Section 6.5.5.3.4, “Rewriter Query Rewrite Plugin Status Variables”.
When you load the rules table by calling the
flush_rewrite_rules() stored procedure, if an
error occurs for some rule, the CALL
statement produces an error, and the plugin sets the
Rewriter_reload_error status variable to
ON:
mysql>CALL query_rewrite.flush_rewrite_rules();ERROR 1644 (45000): Loading of some rule(s) failed. mysql>SHOW GLOBAL STATUS LIKE 'Rewriter_reload_error';+-----------------------+-------+ | Variable_name | Value | +-----------------------+-------+ | Rewriter_reload_error | ON | +-----------------------+-------+
In this case, check the message column of
rewrite_rules table rows for
non-NULL values to see what the problem was.
Rewriter Plugin Use of Character Sets
When the rewrite_rules table is loaded into
the Rewriter plugin, the plugin interprets
statements using the current global value of the
character_set_client system
variable. If the global
character_set_client value is
changed subsequently, the rules table must be reloaded.
A client must have a session
character_set_client value
identical to what the global value was when the rules table was
loaded or rule matching will not work for that client.
The following discussion serves as a reference to these
components associated with the Rewriter query
rewrite plugin:
The
Rewriterrules table in thequery_rewritedatabaseRewriterprocedures and functionsRewritersystem and status variables
The rewrite_rules table in the
query_rewrite database provides persistent
storage for the rules that the Rewriter
plugin uses to decide whether to rewrite statements.
Users communicate with the plugin by modifying the set of
rules stored in this table. The plugin communicates with users
by setting the table's message column.
The rules table is loaded into the plugin by the
flush_rewrite_rules stored procedure.
Unless that procedure has been called following the most
recent table modification, the table contents do not
necessarily correspond to the set of rules the plugin is
using.
The rewrite_rules table has these columns:
idThe rule ID. This column is the table primary key. You can use the ID to uniquely identify any rule.
patternThe template that indicates the pattern for statements that the rule matches. Use
?to represent parameter markers that match data values.pattern_databaseThe database used to match unqualified table names in statements. Qualified table names in statements match qualified names in the pattern if corresponding database and table names are identical. Unqualified table names in statements match unqualified names in the pattern only if the default database is the same as
pattern_databaseand the table names are identical.replacementThe template that indicates how to rewrite statements matching the
patterncolumn value. Use?to represent parameter markers that match data values. In rewritten statements, the plugin replaces?parameter markers inreplacementusing data values matched by the corresponding markers inpattern.enabledWhether the rule is enabled. Load operations (performed by invoking the
flush_rewrite_rules()stored procedure) load the rule from the table into theRewriterin-memory cache only if this column isYES(Ybefore MySQL 5.7.8).This column makes it possible to deactivate a rule without removing it: Set the column to a value other than
YESand reload the table into the plugin.messageThe plugin uses this column for communicating with users. If no error occurs when the rules table is loaded into memory, the plugin sets the
messagecolumn toNULL. A non-NULLvalue indicates an error and the column contents are the error message. Errors can occur under these circumstances:Either the pattern or the replacement is an incorrect SQL statement that produces syntax errors.
The replacement contains more
?parameter markers than the pattern.
If a load error occurs, the plugin also sets the
Rewriter_reload_errorstatus variable toON.pattern_digestThis column is used for debugging and diagnostics. If the column exists when the rules table is loaded into memory, the plugin updates it with the pattern digest. This column may be useful if you are trying to determine why some statement fails to be rewritten.
normalized_patternThis column is used for debugging and diagnostics. If the column exists when the rules table is loaded into memory, the plugin updates it with the normalized form of the pattern. This column may be useful if you are trying to determine why some statement fails to be rewritten.
Before MySQL 5.7.8, the pattern_digest
and normalized_pattern columns are
optional: They are created if you install the
Rewriter plugin using the
install_rewriter_with_optional_columns.sql,
but not if you use
install_rewriter.sql.
Rewriter plugin operation uses a stored
procedure that loads the rules table into its in-memory cache,
and a helper user-defined function (UDF). Under normal
operation, users invoke only the stored procedure. The UDF is
intended to be invoked by the stored procedure, not directly
by users.
flush_rewrite_rules()This stored procedure uses the
load_rewrite_rules()UDF to load the contents of therewrite_rulestable into theRewriterin-memory cache. After loading the table, it also clears the query cache.Calling
flush_rewrite_rules()impliesCOMMIT.Invoke this procedure after you modify the rules table to cause the plugin to update its cache from the new table contents. If any errors occur, the plugin sets the
messagecolumn for the appropriate rule rows in the table and sets theRewriter_reload_errorstatus variable toON.load_rewrite_rules()This UDF is a helper routine used by the
flush_rewrite_rules()stored procedure.
The Rewriter query rewrite plugin supports
the following system variables. These variables are available
only if the plugin is installed (see
Section 6.5.5.1, “Installing or uninstalling the Rewriter Query Rewrite Plugin”).
-
Introduced 5.7.6 System Variable Name rewriter_enabledVariable Scope Global Dynamic Variable Yes Permitted Values Type booleanDefault ONWhether the
Rewriterquery rewrite plugin is enabled. -
Introduced 5.7.6 System Variable Name rewriter_verboseVariable Scope Global Dynamic Variable Yes Permitted Values Type integerFor internal use.
The Rewriter query rewrite plugin supports
the following status variables. These variables are available
only if the plugin is installed (see
Section 6.5.5.1, “Installing or uninstalling the Rewriter Query Rewrite Plugin”).
The number of rewrite plugin rewrite rules successfully loaded from the
rewrite_rulestable into memory for use by theRewriterplugin.The number of times the
rewrite_rulestable has been loaded into the in-memory cache used by theRewriterplugin.Rewriter_number_rewritten_queriesThe number of queries rewritten by the
Rewriterquery rewrite plugin since it was loaded.Whether an error occurred the most recent time that the
rewrite_rulestable was loaded into the in-memory cache used by theRewriterplugin. If the value isOFF, no error occurred. If the value isON, an error occurred; check themessagecolumn of therewriter_rulestable for error messages.
Distributions of MySQL 5.7.8 or higher include Version Tokens, a feature that enables creation of and synchronization around server tokens that applications can use to prevent accessing incorrect or out-of-date data.
The Version Tokens interface has these characteristics:
Version tokens are pairs consisting of a name that serves as a key or identifier, plus a value.
Version tokens can be locked. An application can use token locks to indicate to other cooperating applications that tokens are in use and should not be modified.
Version token lists are established per server; for example, to specify the server assignment or operational state. In addition, an application that communicates with a server can register its own list of tokens that indicate the state it requires the server to be in. An SQL statement sent by the application to a server not in the required state produces an error. This is a signal to the application that it should seek a different server in the required state to receive the SQL statement.
The following sections describe the components of Version Tokens, discuss how to install and use it, and provide reference information for its components.
Version Tokens is based on a plugin library that implements these components:
A server-side plugin named
version_tokensholds the list of version tokens associated with the server and subscribes to notifications for statement execution events. Theversion_tokensplugin uses the audit plugin API to monitor incoming statements from clients and matches each client's session-specific version token list against the server version token list. If there is a match, the plugin lets the statement through and the server continues to process it. Otherwise, the plugin returns an error to the client and the statement fails.A set of user-defined functions (UDFs) provides an SQL-level API for manipulating and inspecting the list of server version tokens maintained by the plugin.
A system variable enables clients to specify the list of version tokens that register the required server state. If the server has a different state when a client sends a statement, the client receives an error.
If installed, Version Tokens involves some overhead. To avoid this overhead, do not install it unless you plan to use it.
This section describes how to install or uninstall Version Tokens, which is implemented in a plugin library file containing a plugin and user-defined functions. For general information about installing or uninstalling plugins and UDFs, see Section 6.5.2, “Installing and Uninstalling Plugins”, and Section 26.4.2.5, “UDF Compiling and Installing”.
To be usable by the server, the plugin library file must be
located in the MySQL plugin directory (the directory named by
the plugin_dir system
variable). If necessary, set the value of
plugin_dir at server startup to
tell the server the plugin directory location.
The plugin library file base name is
version_tokens. The file name suffix differs
per platform (for example, .so for Unix and
Unix-like systems, .dll for Windows).
To install the Version Tokens plugin and UDFs, use the
INSTALL PLUGIN and
CREATE FUNCTION statements
(adjust the .so suffix for your platform as
necessary):
INSTALL PLUGIN version_tokens SONAME 'version_token.so'; CREATE FUNCTION version_tokens_set RETURNS STRING SONAME 'version_token.so'; CREATE FUNCTION version_tokens_show RETURNS STRING SONAME 'version_token.so'; CREATE FUNCTION version_tokens_edit RETURNS STRING SONAME 'version_token.so'; CREATE FUNCTION version_tokens_delete RETURNS STRING SONAME 'version_token.so'; CREATE FUNCTION version_tokens_lock_shared RETURNS INT SONAME 'version_token.so'; CREATE FUNCTION version_tokens_lock_exclusive RETURNS INT SONAME 'version_token.so'; CREATE FUNCTION version_tokens_unlock RETURNS INT SONAME 'version_token.so';
You must install the UDFs to manage the server's version token list, but you must also install the plugin because the UDFs will not work correctly without it.
If the plugin and UDFs are used on a master replication server, install them on all slave servers as well to avoid replication problems.
Once installed as just described, the Version Tokens plugin and
UDFs remain installed until uninstalled. To remove them, use the
UNINSTALL PLUGIN and
DROP FUNCTION statements:
UNINSTALL PLUGIN version_tokens; DROP FUNCTION version_tokens_set; DROP FUNCTION version_tokens_show; DROP FUNCTION version_tokens_edit; DROP FUNCTION version_tokens_delete; DROP FUNCTION version_tokens_lock_shared; DROP FUNCTION version_tokens_lock_exclusive; DROP FUNCTION version_tokens_unlock;
Before using Version Tokens, install it according to the instructions provided at Section 6.5.6.2, “Installing or Uninstalling Version Tokens”.
A scenario in which Version Tokens can be useful is a system that accesses a collection of MySQL servers but needs to manage them for load balancing purposes by monitoring them and adjusting server assignments according to load changes. Such a system comprises these components:
The collection of MySQL servers to be managed.
An administrative or management application that communicates with the servers and organizes them into high-availability groups. Groups serve different purposes, and servers within each group may have different assignments. Assignment of a server within a certain group can change at any time.
Client applications that access the servers to retrieve and update data, choosing servers according to the purposes assigned them. For example, a client should not send an update to a read-only server.
Version Tokens permit server access to be managed according to assignment without requiring clients to repeatedly query the servers about their assignments:
The management application performs server assignments and establishes version tokens on each server to reflect its assignment. The application caches this information to provide a central access point to it.
If at some point the management application needs to change a server assignment (for example, to change it from permitting writes to read only), it changes the server's version token list and updates its cache.
To improve performance, client applications obtain cache information from the management application, enabling them to avoid having to retrieve information about server assignments for each statement. Based on the type of statements it will issue (for example, reads versus writes), a client selects an appropriate server and connects to it.
In addition, the client sends to the server its own client-specific version tokens to register the assignment it requires of the server. For each statement sent by the client to the server, the server compares its own token list with the client token list. If the server token list contains all tokens present in the client token list with the same values, there is a match and the server executes the statement.
On the other hand, perhaps the management application has changed the server assignment and its version token list. In this case, the new server assignment may now be incompatible with the client requirements. A token mismatch between the server and client token lists occurs and the server returns an error in reply to the statement. This is an indication to the client to refresh its version token information from the management application cache, and to select a new server to communicate with.
The client-side logic for detecting version token errors and selecting a new server can be implemented different ways:
The client can handle all version token registration, mismatch detection, and connection switching itself.
The logic for those actions can be implemented in a connector that manages connections between clients and MySQL servers. Such a connector might handle mismatch error detection and statement resending itself, or it might pass the error to the application and leave it to the application to resend the statement.
The following example illustrates the preceding discussion in more concrete form.
When Version Tokens initializes on a given server, the server's
version token list is empty. Token list maintenance is performed
by calling user-defined functions (UDFs). The
SUPER privilege is required to
call any of the Version Token UDFs, so token list modification
is expected to be done by a management or administrative
application that has that privilege.
Suppose that a management application communicates with a set of
servers that are queried by clients to access employee and
product databases (named emp and
prod, respectively). All servers are
permitted to process data retrieval statements, but only some of
them are permitted to make database updates. To handle this on a
database-specific basis, the management application establishes
a list of version tokens on each server. In the token list for a
given server, token names represent database names and token
values are read or write
depending on whether the database must be used in read-only
fashion or whether it can take reads and writes.
Client applications register a list of version tokens they require the server to match by setting a system variable. Variable setting occurs on a client-specific basis, so different clients can register different requirements. By default, the client token list is empty, which matches any server token list. When a client sets its token list to a nonempty value, matching may succeed or fail, depending on the server version token list.
To define the version token list for a server, the management
application calls the version_token_set()
UDF. (There are also UDFs for modifying and displaying the token
list, described later.) For example, the application might send
these statements to a group of three servers:
Server 1:
mysql> SELECT version_tokens_set('emp=read;prod=read');
+------------------------------------------+
| version_tokens_set('emp=read;prod=read') |
+------------------------------------------+
| 2 version tokens set. |
+------------------------------------------+
Server 2:
mysql> SELECT version_tokens_set('emp=write;prod=read');
+-------------------------------------------+
| version_tokens_set('emp=write;prod=read') |
+-------------------------------------------+
| 2 version tokens set. |
+-------------------------------------------+
Server 3:
mysql> SELECT version_tokens_set('emp=read;prod=write');
+-------------------------------------------+
| version_tokens_set('emp=read;prod=write') |
+-------------------------------------------+
| 2 version tokens set. |
+-------------------------------------------+
The token list in each case is specified as a
semicolon-separated list of
name=value
Any server accepts reads for either database.
Only server 2 accepts updates for the
empdatabase.Only server 3 accepts updates for the
proddatabase.
In addition to assigning each server a version token list, the management application also maintains a cache that reflects the server assignments.
Before communicating with the servers, a client application
contacts the management application and retrieves information
about server assignments. Then the client selects a server based
on those assignments. Suppose that a client wants to perform
both reads and writes on the emp database.
Based on the preceding assignments, only server 2 qualifies. The
client connects to server 2 and registers its server
requirements there by setting its
version_tokens_session system variable:
mysql> SET @@session.version_tokens_session = 'emp=write';
For subsequent statements sent by the client to server 2, the server compares its own version token list to the client list to check whether they match. If so, statements execute normally:
mysql>UPDATE emp.employee SET salary = salary * 1.1 WHERE id = 4981;Query OK, 1 row affected (0.07 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql>SELECT last_name, first_name FROM emp.employee WHERE id = 4981;+-----------+------------+ | last_name | first_name | +-----------+------------+ | Smith | Abe | +-----------+------------+ 1 row in set (0.01 sec)
Discrepancies between the server and client version token lists can occur two ways:
A token name in the
version_tokens_sessionvalue is not present in the server token list. In this case, anER_VTOKEN_PLUGIN_TOKEN_NOT_FOUNDerror occurs.A token value in the
version_tokens_sessionvalue differs from the value of the corresponding token in the server token list. In this case, anER_VTOKEN_PLUGIN_TOKEN_MISMATCHerror occurs.
As long as the assignment of server 2 does not change, the
client continues to use it for reads and writes. But suppose
that the management application wants to change server
assignments so that writes for the emp
database must be sent to server 1 instead of server 2. To do
this, it uses version_tokens_edit() to modify
the emp token value on the two servers (and
updates its cache of server assignments):
Server 1:
mysql> SELECT version_tokens_edit('emp=write');
+----------------------------------+
| version_tokens_edit('emp=write') |
+----------------------------------+
| 1 version tokens updated. |
+----------------------------------+
Server 2:
mysql> SELECT version_tokens_edit('emp=read');
+---------------------------------+
| version_tokens_edit('emp=read') |
+---------------------------------+
| 1 version tokens updated. |
+---------------------------------+
version_tokens_edit() modifies the named
tokens in the server token list and leaves other tokens
unchanged.
The next time the client sends a statement to server 2, its own token list no longer matches the server token list and an error occurs:
mysql> UPDATE emp.employee SET salary = salary * 1.1 WHERE id = 4982;
ERROR 3136 (42000): Version token mismatch for emp. Correct value read
In this case, the client should contact the management application to obtain updated information about server assignments, select a new server, and send the failed statement to the new server.
Each client must cooperate with Version Tokens by sending only
statements in accordance with the token list that it registers
with a given server. For example, if a client registers a
token list of 'emp=read', there is nothing
in Version Tokens to prevent the client from sending updates
for the emp database. The client itself
must refrain from doing so.
For each statement received from a client, the server implicitly uses locking, as follows:
Take a shared lock for each token named in the client token list (that is, in the
version_tokens_sessionvalue)Perform the comparison between the server and client token lists
Execute the statement or produce an error depending on the comparison result
Release the locks
The server uses shared locks so that comparisons for multiple sessions can occur without blocking, while preventing changes to the tokens for any session that attempts to acquire an exclusive lock before it manipulates tokens of the same names in the server token list.
The preceding example uses only a few of the user-defined included in the Version Tokens plugin library, but there are others. One set of UDFs permits the server's list of version tokens to be manipulated and inspected. Another set of UDFs permits version tokens to be locked and unlocked.
These UDFs permit the server's list of version tokens to be created, changed, removed, and inspected:
version_tokens_set()completely replaces the current list and assigns a new list. The argument is a semicolon-separated list ofname=valueversion_tokens_edit()enables partial modifications to the current list. It can add new tokens or change the values of existing tokens. The argument is a semicolon-separated list ofname=valueversion_tokens_delete()deletes tokens from the current list. The argument is a semicolon-separated list of token names.version_tokens_show()displays the current token list. It takes no argument.
Each of those functions, if successful, returns a binary string indicating what action occurred. The following example establishes the server token list, modifies it by adding a new token, deletes some tokens, and displays the resulting token list:
mysql>SELECT version_tokens_set('tok1=a;tok2=b');+-------------------------------------+ | version_tokens_set('tok1=a;tok2=b') | +-------------------------------------+ | 2 version tokens set. | +-------------------------------------+ mysql>SELECT version_tokens_edit('tok3=c');+-------------------------------+ | version_tokens_edit('tok3=c') | +-------------------------------+ | 1 version tokens updated. | +-------------------------------+ mysql>SELECT version_tokens_delete('tok2;tok1');+------------------------------------+ | version_tokens_delete('tok2;tok1') | +------------------------------------+ | 2 version tokens deleted. | +------------------------------------+ mysql>SELECT version_tokens_show();+-----------------------+ | version_tokens_show() | +-----------------------+ | tok3=c; | +-----------------------+
Warnings occur if a token list is malformed:
mysql>SELECT version_tokens_set('tok1=a; =c');+----------------------------------+ | version_tokens_set('tok1=a; =c') | +----------------------------------+ | 1 version tokens set. | +----------------------------------+ 1 row in set, 1 warning (0.00 sec) mysql>SHOW WARNINGS\G*************************** 1. row *************************** Level: Warning Code: 42000 Message: Invalid version token pair encountered. The list provided is only partially updated. 1 row in set (0.00 sec)
As mentioned previously, version tokens are defined using a
semicolon-separated list of
name=valueversion_tokens_set():
mysql> SELECT version_tokens_set('tok1=b;;; tok2= a = b ; tok1 = 1\'2 3"4')
+---------------------------------------------------------------+
| version_tokens_set('tok1=b;;; tok2= a = b ; tok1 = 1\'2 3"4') |
+---------------------------------------------------------------+
| 3 version tokens set. |
+---------------------------------------------------------------+
Version Tokens interprets the argument as follows:
Whitespace around names and values is ignored. Whitespace within names and values is permitted. (For
version_tokens_delete(), which takes a list of names without values, whitespace around names is ignored.)There is no quoting mechanism.
Order of tokens is not significant except that if a token list contains multiple instances of a given token name, the last value takes precedence over earlier values.
Given those rules, the preceding
version_tokens_set() call results in a token
list with two tokens: tok1 has the value
1'2 3"4, and tok2 has the
value a = b. To verify this, call
version_tokens_show():
mysql> SELECT version_tokens_show();
+--------------------------+
| version_tokens_show() |
+--------------------------+
| tok2=a = b;tok1=1'2 3"4; |
+--------------------------+
If the token list contains two tokens, why did
version_tokens_set() return the value
3 version tokens set? That occurred because
the original token list contained two definitions for
tok1, and the second definition replaced the
first.
The Version Tokens token-manipulation UDFs place these constraints on token names and values:
Token names cannot contain
=or;characters and have a maximum length of 64 characters.Token values cannot contain
;characters. Length of values is constrained by the value of themax_allowed_packetsystem variable.Version Tokens treats token names and values as binary strings, so comparisons are case sensitive.
Version Tokens also includes a set of UDFs enabling tokens to be locked and unlocked:
version_tokens_lock_exclusive()acquires exclusive version token locks. It takes a list of one or more lock names and a timeout value.version_tokens_lock_shared()acquires shared version token locks. It takes a list of one or more lock names and a timeout value.version_tokens_unlock()releases version token locks (exclusive and shared). It takes no argument.
Each locking function returns nonzero for success. Otherwise, an error occurs:
mysql>SELECT version_tokens_lock_shared('lock1', 'lock2', 0);+-------------------------------------------------+ | version_tokens_lock_shared('lock1', 'lock2', 0) | +-------------------------------------------------+ | 1 | +-------------------------------------------------+ mysql>SELECT version_tokens_lock_shared(NULL, 0);ERROR 3131 (42000): Incorrect locking service lock name '(null)'.
Locking using Version Tokens locking functions is advisory; applications must agree to cooperate.
It is possible to lock nonexisting token names. This does not create the tokens.
Version Tokens locking functions are based on the locking
service described at Section 26.3.1, “The Locking Service”, and
thus have the same semantics for shared and exclusive locks.
(Version Tokens uses the locking service routines built into
the server, not the locking service UDF interface, so those
UDFs need not be installed to use Version Tokens.) Locks
acquired by Version Tokens use a locking service namespace of
version_token_locks. Locking service locks
can be monitored using the Performance Schema, so this is also
true for Version Tokens locks. For details, see
Section 26.3.1.2.3, “Locking Service Monitoring”.
For the Version Tokens locking functions, token name arguments
are used exactly as specified. Surrounding whitespace is not
ignored and = and ;
characters are permitted. This is because Version Tokens simply
passes the token names to be locked as is to the locking
service.
The following discussion serves as a reference to these Version Tokens components:
Version Tokens user-defined functions
Version Tokens system variables
The Version Tokens plugin library includes several
user-defined functions. One set of UDFs permits the server's
list of version tokens to be manipulated and inspected.
Another set of UDFs permits version tokens to be locked and
unlocked. The SUPER privilege
is required to invoke any Version Tokens UDF.
The following UDFs permit the server's list of version tokens
to be created, changed, removed, and inspected. Interpretation
of name_list and
token_list arguments (including
whitespace handling) occurs as described in
Section 6.5.6.3, “Using Version Tokens”, which provides details
about the syntax for specifying tokens, as well as additional
examples.
version_tokens_delete(name_list)Deletes tokens from the server's list of version tokens using the
name_listargument and returns a binary string that indicates the outcome of the operation.name_listis a semicolon-separated list of version token names to delete.mysql>
SELECT version_tokens_delete('tok1;tok3');+------------------------------------+ | version_tokens_delete('tok1;tok3') | +------------------------------------+ | 2 version tokens deleted. | +------------------------------------+As of MySQL 5.7.9, an argument of
NULLis treated as an empty string, which has no effect on the token list.version_tokens_delete()deletes the tokens named in its argument, if they exist. (It is not an error to delete nonexisting tokens.) To clear the token list entirely without knowing which tokens are in the list, passNULLor a string containing no tokens toversion_tokens_set():mysql>
SELECT version_tokens_set(NULL);+------------------------------+ | version_tokens_set(NULL) | +------------------------------+ | Version tokens list cleared. | +------------------------------+ mysql>SELECT version_tokens_set('');+------------------------------+ | version_tokens_set('') | +------------------------------+ | Version tokens list cleared. | +------------------------------+version_tokens_edit(token_list)Modifies the server's list of version tokens using the
token_listargument and returns a binary string that indicates the outcome of the operation.token_listis a semicolon-separated list ofname=valueNULLor a string containing no tokens, the token list remains unchanged.mysql>
SELECT version_tokens_set('tok1=value1;tok2=value2');+-----------------------------------------------+ | version_tokens_set('tok1=value1;tok2=value2') | +-----------------------------------------------+ | 2 version tokens set. | +-----------------------------------------------+ mysql>SELECT version_tokens_edit('tok2=new_value2;tok3=new_value3');+--------------------------------------------------------+ | version_tokens_edit('tok2=new_value2;tok3=new_value3') | +--------------------------------------------------------+ | 2 version tokens updated. | +--------------------------------------------------------+version_tokens_set(token_list)Replaces the server's list of version tokens with the tokens defined in the
token_listargument and returns a binary string that indicates the outcome of the operation.token_listis a semicolon-separated list ofname=valueNULLor a string containing no tokens, the token list is cleared.mysql>
SELECT version_tokens_set('tok1=value1;tok2=value2');+-----------------------------------------------+ | version_tokens_set('tok1=value1;tok2=value2') | +-----------------------------------------------+ | 2 version tokens set. | +-----------------------------------------------+version_tokens_show()Returns the server's list of version tokens as a binary string containing a semicolon-separated list of
name=valuemysql>
SELECT version_tokens_show();+--------------------------+ | version_tokens_show() | +--------------------------+ | tok2=value2;tok1=value1; | +--------------------------+
The following UDFs permit version tokens to be locked and unlocked:
version_tokens_lock_exclusive(token_name[,token_name] ...,timeout)Acquires exclusive locks on one or more version tokens, specified by name as strings, timing out with an error if the locks are not acquired within the given timeout value.
mysql>
SELECT version_tokens_lock_exclusive('lock1', 'lock2', 10);+-----------------------------------------------------+ | version_tokens_lock_exclusive('lock1', 'lock2', 10) | +-----------------------------------------------------+ | 1 | +-----------------------------------------------------+This function was added in MySQL 5.7.8 with the name
vtoken_get_write_locks()and renamed toversion_tokens_lock_exclusive()in 5.7.9.version_tokens_lock_shared(token_name[,token_name] ...,timeout)Acquires shared locks on one or more version tokens, specified by name as strings, timing out with an error if the locks are not acquired within the given timeout value.
mysql>
SELECT version_tokens_lock_shared('lock1', 'lock2', 10);+--------------------------------------------------+ | version_tokens_lock_shared('lock1', 'lock2', 10) | +--------------------------------------------------+ | 1 | +--------------------------------------------------+This function was added in MySQL 5.7.8 with the name
vtoken_get_read_locks()and renamed toversion_tokens_lock_shared()in 5.7.9.version_tokens_unlock()Releases all locks that were acquired within the current session using
version_tokens_lock_exclusive()andversion_tokens_lock_shared().mysql>
SELECT version_tokens_unlock();+-------------------------+ | version_tokens_unlock() | +-------------------------+ | 1 | +-------------------------+This function was added in MySQL 5.7.8 with the name
vtoken_release_locks()and renamed toversion_tokens_unlock()in 5.7.9.
The locking functions share these characteristics:
The return value is nonzero for success. Otherwise, an error occurs.
Token names are strings.
In contrast to argument handling for the UDFs that manipulate the server token list, whitespace surrounding token name arguments is not ignored and
=and;characters are permitted.It is possible to lock nonexisting token names. This does not create the tokens.
Timeout values are nonnegative integers representing the time in seconds to wait to acquire locks before timing out with an error. If the timeout is 0, there is no waiting and the function produces an error if locks cannot be acquired immediately.
Version Tokens locking functions are based on the locking service described at Section 26.3.1, “The Locking Service”.
Version Tokens supports the following system variables. These variables are unavailable unless the Version Tokens plugin is installed (see Section 6.5.6.2, “Installing or Uninstalling Version Tokens”).
System variables:
-
Introduced 5.7.8 Command-Line Format --version_tokens_session=valueSystem Variable Name version_tokens_sessionVariable Scope Global, Session Dynamic Variable Yes Permitted Values Type stringDefault NULLThe session value of this variable specifies the client version token list and indicates the tokens that the client session requires the server version token list to have.
If the
version_tokens_sessionvariable isNULL(the default) or has an empty value, any server version token list matches. (In effect, an empty value disables matching requirements.)If the
version_tokens_sessionvariable has a nonempty value, any mismatch between its value and the server version token list results in an error for any statement the session sends to the server. A mismatch occurs under these conditions:A token name in the
version_tokens_sessionvalue is not present in the server token list. In this case, anER_VTOKEN_PLUGIN_TOKEN_NOT_FOUNDerror occurs.A token value in the
version_tokens_sessionvalue differs from the value of the corresponding token in the server token list. In this case, anER_VTOKEN_PLUGIN_TOKEN_MISMATCHerror occurs.
It is not a mismatch for the server version token list to include a token not named in the
version_tokens_sessionvalue.Suppose that a management application has set the server token list as follows:
mysql>
SELECT version_tokens_set('tok1=a;tok2=b;tok3=c');+--------------------------------------------+ | version_tokens_set('tok1=a;tok2=b;tok3=c') | +--------------------------------------------+ | 3 version tokens set. | +--------------------------------------------+A client registers the tokens it requires the server to match by setting its
version_tokens_sessionvalue. Then, for each subsequent statement sent by the client, the server checks its token list against the clientversion_tokens_sessionvalue and produces an error if there is a mismatch:mysql>
SET @@session.version_tokens_session = 'tok1=a;tok2=b';mysql>SELECT 1;+---+ | 1 | +---+ | 1 | +---+ mysql>SET @@session.version_tokens_session = 'tok1=b';mysql>SELECT 1;ERROR 3136 (42000): Version token mismatch for tok1. Correct value aThe first
SELECTsucceeds because the client tokenstok1andtok2are present in the server token list and each token has the same value in the server list. The secondSELECTfails because, althoughtok1is present in the server token list, it has a different value than specified by the client.At this point, any statement sent by the client fails, unless the server token list changes such that it matches again. Suppose that the management application changes the server token list as follows:
mysql>
SELECT version_tokens_edit('tok1=b');+-------------------------------+ | version_tokens_edit('tok1=b') | +-------------------------------+ | 1 version tokens updated. | +-------------------------------+ mysql>SELECT version_tokens_show();+-----------------------+ | version_tokens_show() | +-----------------------+ | tok3=c;tok1=b;tok2=b; | +-----------------------+Now the client
version_tokens_sessionvalue matches the server token list and the client can once again successfully execute statements:mysql>
SELECT 1;+---+ | 1 | +---+ | 1 | +---+This variable was added in MySQL 5.7.8.
-
Introduced 5.7.8 Command-Line Format --version_tokens_session_number=NSystem Variable Name version_tokens_session_numberVariable Scope Global, Session Dynamic Variable No Permitted Values Type integerDefault 0This variable is for internal use.
This variable was added in MySQL 5.7.8.
In some cases, you might want to run multiple instances of MySQL on a single machine. You might want to test a new MySQL release while leaving an existing production setup undisturbed. Or you might want to give different users access to different mysqld servers that they manage themselves. (For example, you might be an Internet Service Provider that wants to provide independent MySQL installations for different customers.)
It is possible to use a different MySQL server binary per instance, or use the same binary for multiple instances, or any combination of the two approaches. For example, you might run a server from MySQL 5.6 and one from MySQL 5.7, to see how different versions handle a given workload. Or you might run multiple instances of the current production version, each managing a different set of databases.
Whether or not you use distinct server binaries, each instance that
you run must be configured with unique values for several operating
parameters. This eliminates the potential for conflict between
instances. Parameters can be set on the command line, in option
files, or by setting environment variables. See
Section 5.2.3, “Specifying Program Options”. To see the values used by a given
instance, connect to it and execute a SHOW
VARIABLES statement.
The primary resource managed by a MySQL instance is the data
directory. Each instance should use a different data directory, the
location of which is specified using the
--datadir=
option. For methods of configuring each instance with its own data
directory, and warnings about the dangers of failing to do so, see
Section 6.6.1, “Setting Up Multiple Data Directories”.
dir_name
In addition to using different data directories, several other options must have different values for each server instance:
--portcontrols the port number for TCP/IP connections. Alternatively, if the host has multiple network addresses, you can use--bind-addressto cause each server to listen to a different address.--socket={file_name|pipe_name}--socketcontrols the Unix socket file path on Unix or the named pipe name on Windows. On Windows, it is necessary to specify distinct pipe names only for those servers configured to permit named-pipe connections.--shared-memory-base-name=nameThis option is used only on Windows. It designates the shared-memory name used by a Windows server to permit clients to connect using shared memory. It is necessary to specify distinct shared-memory names only for those servers configured to permit shared-memory connections.
This option indicates the path name of the file in which the server writes its process ID.
If you use the following log file options, their values must differ for each server:
For further discussion of log file options, see Section 6.4, “MySQL Server Logs”.
To achieve better performance, you can specify the following option differently for each server, to spread the load between several physical disks:
Having different temporary directories also makes it easier to determine which MySQL server created any given temporary file.
If you have multiple MySQL installations in different locations, you
can specify the base directory for each installation with the
--basedir=
option. This causes each instance to automatically use a different
data directory, log files, and PID file because the default for each
of those parameters is relative to the base directory. In that case,
the only other options you need to specify are the
dir_name--socket and
--port options. Suppose that you
install different versions of MySQL using tar
file binary distributions. These install in different locations, so
you can start the server for each installation using the command
bin/mysqld_safe under its corresponding base
directory. mysqld_safe determines the proper
--basedir option to pass to
mysqld, and you need specify only the
--socket and
--port options to
mysqld_safe.
As discussed in the following sections, it is possible to start
additional servers by specifying appropriate command options or by
setting environment variables. However, if you need to run multiple
servers on a more permanent basis, it is more convenient to use
option files to specify for each server those option values that
must be unique to it. The
--defaults-file option is useful for
this purpose.
Each MySQL Instance on a machine should have its own data
directory. The location is specified using the
--datadir=
option.
dir_name
There are different methods of setting up a data directory for a new instance:
Create a new data directory.
Copy an existing data directory.
The following discussion provides more detail about each method.
Normally, you should never have two servers that update data in the same databases. This may lead to unpleasant surprises if your operating system does not support fault-free system locking. If (despite this warning) you run multiple servers using the same data directory and they have logging enabled, you must use the appropriate options to specify log file names that are unique to each server. Otherwise, the servers try to log to the same files.
Even when the preceding precautions are observed, this kind of
setup works only with MyISAM and
MERGE tables, and not with any of the other
storage engines. Also, this warning against sharing a data
directory among servers always applies in an NFS environment.
Permitting multiple MySQL servers to access a common data
directory over NFS is a very bad idea. The
primary problem is that NFS is the speed bottleneck. It is not
meant for such use. Another risk with NFS is that you must
devise a way to ensure that two or more servers do not interfere
with each other. Usually NFS file locking is handled by the
lockd daemon, but at the moment there is no
platform that performs locking 100% reliably in every situation.
Create a New Data Directory
With this method, the data directory will be in the same state as when you first install MySQL. It will have the default set of MySQL accounts and no user data.
On Unix, initialize the data directory. See Section 2.10, “Postinstallation Setup and Testing”.
On Windows, the data directory is included in the MySQL distribution:
MySQL Zip archive distributions for Windows contain an unmodified data directory. You can unpack such a distribution into a temporary location, then copy it
datadirectory to where you are setting up the new instance.Windows MSI package installers create and set up the data directory that the installed server will use, but also create a pristine “template” data directory named
dataunder the installation directory. After an installation has been performed using an MSI package, the template data directory can be copied to set up additional MySQL instances.
Copy an Existing Data Directory
With this method, any MySQL accounts or user data present in the data directory are carried over to the new data directory.
Stop the existing MySQL instance using the data directory. This must be a clean shutdown so that the instance flushes any pending changes to disk.
Copy the data directory to the location where the new data directory should be.
Copy the
my.cnformy.inioption file used by the existing instance. This serves as a basis for the new instance.Modify the new option file so that any pathnames referring to the original data directory refer to the new data directory. Also, modify any other options that must be unique per instance, such as the TCP/IP port number and the log files. For a list of parameters that must be unique per instance, see Section 6.6, “Running Multiple MySQL Instances on One Machine”.
Start the new instance, telling it to use the new option file.
You can run multiple servers on Windows by starting them manually from the command line, each with appropriate operating parameters, or by installing several servers as Windows services and running them that way. General instructions for running MySQL from the command line or as a service are given in Section 2.3, “Installing MySQL on Microsoft Windows”. The following sections describe how to start each server with different values for those options that must be unique per server, such as the data directory. These options are listed in Section 6.6, “Running Multiple MySQL Instances on One Machine”.
The procedure for starting a single MySQL server manually from
the command line is described in
Section 2.3.5.6, “Starting MySQL from the Windows Command Line”. To start multiple
servers this way, you can specify the appropriate options on the
command line or in an option file. It is more convenient to
place the options in an option file, but it is necessary to make
sure that each server gets its own set of options. To do this,
create an option file for each server and tell the server the
file name with a --defaults-file
option when you run it.
Suppose that you want to run one instance of
mysqld on port 3307 with a data directory of
C:\mydata1, and another instance on port
3308 with a data directory of C:\mydata2.
Use this procedure:
Make sure that each data directory exists, including its own copy of the
mysqldatabase that contains the grant tables.Create two option files. For example, create one file named
C:\my-opts1.cnfthat looks like this:[mysqld] datadir = C:/mydata1 port = 3307
Create a second file named
C:\my-opts2.cnfthat looks like this:[mysqld] datadir = C:/mydata2 port = 3308
Use the
--defaults-fileoption to start each server with its own option file:C:\>
C:\mysql\bin\mysqld --defaults-file=C:\my-opts1.cnfC:\>C:\mysql\bin\mysqld --defaults-file=C:\my-opts2.cnfEach server starts in the foreground (no new prompt appears until the server exits later), so you will need to issue those two commands in separate console windows.
To shut down the servers, connect to each using the appropriate port number:
C:\>C:\mysql\bin\mysqladmin --port=3307 --host=127.0.0.1 --user=root --password shutdownC:\>C:\mysql\bin\mysqladmin --port=3308 --host=127.0.0.1 --user=root --password shutdown
Servers configured as just described permit clients to connect
over TCP/IP. If your version of Windows supports named pipes and
you also want to permit named-pipe connections, specify options
that enable the named pipe and specify its name. Each server
that supports named-pipe connections must use a unique pipe
name. For example, the C:\my-opts1.cnf file
might be written like this:
[mysqld] datadir = C:/mydata1 port = 3307 enable-named-pipe socket = mypipe1
Modify C:\my-opts2.cnf similarly for use by
the second server. Then start the servers as described
previously.
A similar procedure applies for servers that you want to permit
shared-memory connections. Enable such connections with the
--shared-memory option and
specify a unique shared-memory name for each server with the
--shared-memory-base-name option.
On Windows, a MySQL server can run as a Windows service. The procedures for installing, controlling, and removing a single MySQL service are described in Section 2.3.5.8, “Starting MySQL as a Windows Service”.
To set up multiple MySQL services, you must make sure that each instance uses a different service name in addition to the other parameters that must be unique per instance.
For the following instructions, suppose that you want to run the
mysqld server from two different versions of
MySQL that are installed at C:\mysql-5.5.9
and C:\mysql-5.7.15,
respectively. (This might be the case if you are running 5.5.9
as your production server, but also want to conduct tests using
5.7.15.)
To install MySQL as a Windows service, use the
--install or --install-manual
option. For information about these options, see
Section 2.3.5.8, “Starting MySQL as a Windows Service”.
Based on the preceding information, you have several ways to set up multiple services. The following instructions describe some examples. Before trying any of them, shut down and remove any existing MySQL services.
Approach 1: Specify the options for all services in one of the standard option files. To do this, use a different service name for each server. Suppose that you want to run the 5.5.9 mysqld using the service name of
mysqld1and the 5.7.15 mysqld using the service namemysqld2. In this case, you can use the[mysqld1]group for 5.5.9 and the[mysqld2]group for 5.7.15. For example, you can set upC:\my.cnflike this:# options for mysqld1 service [mysqld1] basedir = C:/mysql-5.5.9 port = 3307 enable-named-pipe socket = mypipe1 # options for mysqld2 service [mysqld2] basedir = C:/mysql-5.7.15 port = 3308 enable-named-pipe socket = mypipe2
Install the services as follows, using the full server path names to ensure that Windows registers the correct executable program for each service:
C:\>
C:\mysql-5.5.9\bin\mysqld --install mysqld1C:\>C:\mysql-5.7.15\bin\mysqld --install mysqld2To start the services, use the services manager, or use NET START with the appropriate service names:
C:\>
NET START mysqld1C:\>NET START mysqld2To stop the services, use the services manager, or use NET STOP with the appropriate service names:
C:\>
NET STOP mysqld1C:\>NET STOP mysqld2Approach 2: Specify options for each server in separate files and use
--defaults-filewhen you install the services to tell each server what file to use. In this case, each file should list options using a[mysqld]group.With this approach, to specify options for the 5.5.9 mysqld, create a file
C:\my-opts1.cnfthat looks like this:[mysqld] basedir = C:/mysql-5.5.9 port = 3307 enable-named-pipe socket = mypipe1
For the 5.7.15 mysqld, create a file
C:\my-opts2.cnfthat looks like this:[mysqld] basedir = C:/mysql-5.7.15 port = 3308 enable-named-pipe socket = mypipe2
Install the services as follows (enter each command on a single line):
C:\>
C:\mysql-5.5.9\bin\mysqld --install mysqld1--defaults-file=C:\my-opts1.cnfC:\>C:\mysql-5.7.15\bin\mysqld --install mysqld2--defaults-file=C:\my-opts2.cnfWhen you install a MySQL server as a service and use a
--defaults-fileoption, the service name must precede the option.After installing the services, start and stop them the same way as in the preceding example.
To remove multiple services, use mysqld
--remove for each one, specifying a service name
following the --remove option. If
the service name is the default (MySQL), you
can omit it.
One way is to run multiple MySQL instances on Unix is to compile different servers with different default TCP/IP ports and Unix socket files so that each one listens on different network interfaces. Compiling in different base directories for each installation also results automatically in a separate, compiled-in data directory, log file, and PID file location for each server.
Assume that an existing 5.6 server is configured for
the default TCP/IP port number (3306) and Unix socket file
(/tmp/mysql.sock). To configure a new
5.7.15 server to have different operating parameters,
use a CMake command something like this:
shell>cmake . -DMYSQL_TCP_PORT=port_number\-DMYSQL_UNIX_ADDR=file_name\-DCMAKE_INSTALL_PREFIX=/usr/local/mysql-5.7.15
Here, port_number and
file_name must be different from the
default TCP/IP port number and Unix socket file path name, and the
CMAKE_INSTALL_PREFIX value should
specify an installation directory different from the one under
which the existing MySQL installation is located.
If you have a MySQL server listening on a given port number, you can use the following command to find out what operating parameters it is using for several important configurable variables, including the base directory and Unix socket file name:
shell> mysqladmin --host=host_name --port=port_number variables
With the information displayed by that command, you can tell what option values not to use when configuring an additional server.
If you specify localhost as the host name,
mysqladmin defaults to using a Unix socket file
connection rather than TCP/IP. To explicitly specify the
connection protocol, use the
--protocol={TCP|SOCKET|PIPE|MEMORY}
option.
You need not compile a new MySQL server just to start with a different Unix socket file and TCP/IP port number. It is also possible to use the same server binary and start each invocation of it with different parameter values at runtime. One way to do so is by using command-line options:
shell> mysqld_safe --socket=file_name --port=port_number
To start a second server, provide different
--socket and
--port option values, and pass a
--datadir=
option to mysqld_safe so that the server uses a
different data directory.
dir_name
Alternatively, put the options for each server in a different
option file, then start each server using a
--defaults-file option that
specifies the path to the appropriate option file. For example, if
the option files for two server instances are named
/usr/local/mysql/my.cnf and
/usr/local/mysql/my.cnf2, start the servers
like this: command:
shell>mysqld_safe --defaults-file=/usr/local/mysql/my.cnfshell>mysqld_safe --defaults-file=/usr/local/mysql/my.cnf2
Another way to achieve a similar effect is to use environment variables to set the Unix socket file name and TCP/IP port number:
shell>MYSQL_UNIX_PORT=/tmp/mysqld-new.sockshell>MYSQL_TCP_PORT=3307shell>export MYSQL_UNIX_PORT MYSQL_TCP_PORTshell>mysql_install_db --user=mysqlshell>mysqld_safe --datadir=/path/to/datadir &
This is a quick way of starting a second server to use for testing. The nice thing about this method is that the environment variable settings apply to any client programs that you invoke from the same shell. Thus, connections for those clients are automatically directed to the second server.
Section 2.12, “Environment Variables”, includes a list of other environment variables you can use to affect MySQL programs.
On Unix, the mysqld_multi script provides another way to start multiple servers. See Section 5.3.4, “mysqld_multi — Manage Multiple MySQL Servers”.
To connect with a client program to a MySQL server that is listening to different network interfaces from those compiled into your client, you can use one of the following methods:
Start the client with
--host=host_name--port=to connect using TCP/IP to a remote server, withport_number--host=127.0.0.1--port=to connect using TCP/IP to a local server, or withport_number--host=localhost--socket=to connect to a local server using a Unix socket file or a Windows named pipe.file_nameStart the client with
--protocol=TCPto connect using TCP/IP,--protocol=SOCKETto connect using a Unix socket file,--protocol=PIPEto connect using a named pipe, or--protocol=MEMORYto connect using shared memory. For TCP/IP connections, you may also need to specify--hostand--portoptions. For the other types of connections, you may need to specify a--socketoption to specify a Unix socket file or Windows named-pipe name, or a--shared-memory-base-nameoption to specify the shared-memory name. Shared-memory connections are supported only on Windows.On Unix, set the
MYSQL_UNIX_PORTandMYSQL_TCP_PORTenvironment variables to point to the Unix socket file and TCP/IP port number before you start your clients. If you normally use a specific socket file or port number, you can place commands to set these environment variables in your.loginfile so that they apply each time you log in. See Section 2.12, “Environment Variables”.Specify the default Unix socket file and TCP/IP port number in the
[client]group of an option file. For example, you can useC:\my.cnfon Windows, or the.my.cnffile in your home directory on Unix. See Section 5.2.6, “Using Option Files”.In a C program, you can specify the socket file or port number arguments in the
mysql_real_connect()call. You can also have the program read option files by callingmysql_options(). See Section 25.8.7, “C API Function Descriptions”.If you are using the Perl
DBD::mysqlmodule, you can read options from MySQL option files. For example:$dsn = "DBI:mysql:test;mysql_read_default_group=client;" . "mysql_read_default_file=/usr/local/mysql/data/my.cnf"; $dbh = DBI->connect($dsn, $user, $password);See Section 25.10, “MySQL Perl API”.
Other programming interfaces may provide similar capabilities for reading option files.
The DTrace probes in the MySQL server are designed to provide
information about the execution of queries within MySQL and the
different areas of the system being utilized during that process.
The organization and triggering of the probes means that the
execution of an entire query can be monitored with one level of
probes (query-start and
query-done) but by monitoring other probes you
can get successively more detailed information about the execution
of the query in terms of the locks used, sort methods and even
row-by-row and storage-engine level execution information.
The DTrace probes are organized so that you can follow the entire query process, from the point of connection from a client, through the query execution, row-level operations, and back out again. You can think of the probes as being fired within a specific sequence during a typical client connect/execute/disconnect sequence, as shown in the following figure.
Global information is provided in the arguments to the DTrace probes
at various levels. Global information, that is, the connection ID
and user/host and where relevant the query string, is provided at
key levels (connection-start,
command-start, query-start,
and query-exec-start). As you go deeper into the
probes, it is assumed either you are only interested in the
individual executions (row-level probes provide information on the
database and table name only), or that you will combine the
row-level probes with the notional parent probes to provide the
information about a specific query. Examples of this will be given
as the format and arguments of each probe are provided.
MySQL includes support for DTrace probes on these platforms:
Solaris 10 Update 5 (Solaris 5/08) on SPARC, x86 and x86_64 platforms
OS X 10.4 and higher
Oracle Linux 6 and higher with UEK kernel (as of MySQL 5.7.5)
Enabling the probes should be automatic on these platforms. To
explicitly enable or disable the probes during building, use the
-DENABLE_DTRACE=1 or
-DENABLE_DTRACE=0 option to
CMake.
If a non-Solaris platform includes DTrace support, building mysqld on that platform will include DTrace support.
Additional Resources
For more information on DTrace and writing DTrace scripts, read the DTrace User Guide.
For an introduction to DTrace, see the MySQL Dev Zone article Getting started with DTracing MySQL.
- 6.7.1.1 Connection Probes
- 6.7.1.2 Command Probes
- 6.7.1.3 Query Probes
- 6.7.1.4 Query Parsing Probes
- 6.7.1.5 Query Cache Probes
- 6.7.1.6 Query Execution Probes
- 6.7.1.7 Row-Level Probes
- 6.7.1.8 Read Row Probes
- 6.7.1.9 Index Probes
- 6.7.1.10 Lock Probes
- 6.7.1.11 Filesort Probes
- 6.7.1.12 Statement Probes
- 6.7.1.13 Network Probes
- 6.7.1.14 Keycache Probes
MySQL supports the following static probes, organized into groups of functionality.
Table 6.5 MySQL DTrace Probes
| Group | Probes |
|---|---|
| Connection | connection-start, connection-done |
| Command | command-start, command-done |
| Query | query-start, query-done |
| Query Parsing | query-parse-start,
query-parse-done |
| Query Cache | query-cache-hit, query-cache-miss |
| Query Execution | query-exec-start, query-exec-done |
| Row Level | insert-row-start, insert-row-done |
update-row-start, update-row-done | |
delete-row-start, delete-row-done | |
| Row Reads | read-row-start, read-row-done |
| Index Reads | index-read-row-start,
index-read-row-done |
| Lock | handler-rdlock-start,
handler-rdlock-done |
handler-wrlock-start,
handler-wrlock-done | |
handler-unlock-start,
handler-unlock-done | |
| Filesort | filesort-start, filesort-done |
| Statement | select-start, select-done |
insert-start, insert-done | |
insert-select-start,
insert-select-done | |
update-start, update-done | |
multi-update-start,
multi-update-done | |
delete-start, delete-done | |
multi-delete-start,
multi-delete-done | |
| Network | net-read-start, net-read-done,
net-write-start,
net-write-done |
| Keycache | keycache-read-start,
keycache-read-block,
keycache-read-done,
keycache-read-hit,
keycache-read-miss,
keycache-write-start,
keycache-write-block,
keycache-write-done |
When extracting the argument data from the probes, each argument
is available as
arg, starting
with Narg0. To identify each argument within
the definitions they are provided with a descriptive name, but
you must access the information using the corresponding
arg parameter.
N
The connection-start and
connection-done probes enclose a connection
from a client, regardless of whether the connection is through a
socket or network connection.
connection-start(connectionid, user, host) connection-done(status, connectionid)
connection-start: Triggered after a connection and successful login/authentication have been completed by a client. The arguments contain the connection information:connectionid: Anunsigned longcontaining the connection ID. This is the same as the process ID shown as theIdvalue in the output fromSHOW PROCESSLIST.user: The username used when authenticating. The value will be blank for the anonymous user.host: The host of the client connection. For a connection made using UNIX sockets, the value will be blank.
connection-done: Triggered just as the connection to the client has been closed. The arguments are:status: The status of the connection when it was closed. A logout operation will have a value of 0; any other termination of the connection has a nonzero value.connectionid: The connection ID of the connection that was closed.
The following D script will quantify and summarize the average duration of individual connections, and provide a count, dumping the information every 60 seconds:
#!/usr/sbin/dtrace -s
mysql*:::connection-start
{
self->start = timestamp;
}
mysql*:::connection-done
/self->start/
{
@ = quantize(((timestamp - self->start)/1000000));
self->start = 0;
}
tick-60s
{
printa(@);
}
When executed on a server with a large number of clients you might see output similar to this:
1 57413 :tick-60s
value ------------- Distribution ------------- count
-1 | 0
0 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 30011
1 | 59
2 | 5
4 | 20
8 | 29
16 | 18
32 | 27
64 | 30
128 | 11
256 | 10
512 | 1
1024 | 6
2048 | 8
4096 | 9
8192 | 8
16384 | 2
32768 | 1
65536 | 1
131072 | 0
262144 | 1
524288 | 0
The command probes are executed before and after a client
command is executed, including any SQL statement that might be
executed during that period. Commands include operations such as
the initialization of the DB, use of the
COM_CHANGE_USER operation (supported by the
MySQL protocol), and manipulation of prepared statements. Many
of these commands are used only by the MySQL client API from
various connectors such as PHP and Java.
command-start(connectionid, command, user, host) command-done(status)
command-start: Triggered when a command is submitted to the server.connectionid: The connection ID of the client executing the command.command: An integer representing the command that was executed. Possible values are shown in the following table.Value Name Description 00 COM_SLEEP Internal thread state 01 COM_QUIT Close connection 02 COM_INIT_DB Select database ( USE ...)03 COM_QUERY Execute a query 04 COM_FIELD_LIST Get a list of fields 05 COM_CREATE_DB Create a database (deprecated) 06 COM_DROP_DB Drop a database (deprecated) 07 COM_REFRESH Refresh connection 08 COM_SHUTDOWN Shutdown server 09 COM_STATISTICS Get statistics 10 COM_PROCESS_INFO Get processes ( SHOW PROCESSLIST)11 COM_CONNECT Initialize connection 12 COM_PROCESS_KILL Kill process 13 COM_DEBUG Get debug information 14 COM_PING Ping 15 COM_TIME Internal thread state 16 COM_DELAYED_INSERT Internal thread state 17 COM_CHANGE_USER Change user 18 COM_BINLOG_DUMP Used by a replication slave or mysqlbinlog to initiate a binary log read 19 COM_TABLE_DUMP Used by a replication slave to get the master table information 20 COM_CONNECT_OUT Used by a replication slave to log a connection to the server 21 COM_REGISTER_SLAVE Used by a replication slave during registration 22 COM_STMT_PREPARE Prepare a statement 23 COM_STMT_EXECUTE Execute a statement 24 COM_STMT_SEND_LONG_DATA Used by a client when requesting extended data 25 COM_STMT_CLOSE Close a prepared statement 26 COM_STMT_RESET Reset a prepared statement 27 COM_SET_OPTION Set a server option 28 COM_STMT_FETCH Fetch a prepared statement user: The user executing the command.host: The client host.
command-done: Triggered when the command execution completes. Thestatusargument contains 0 if the command executed successfully, or 1 if the statement was terminated before normal completion.
The command-start and
command-done probes are best used when
combined with the statement probes to get an idea of overall
execution time.
The query-start and
query-done probes are triggered when a
specific query is received by the server and when the query has
been completed and the information has been successfully sent to
the client.
query-start(query, connectionid, database, user, host) query-done(status)
query-start: Triggered after the query string has been received from the client. The arguments are:query: The full text of the submitted query.connectionid: The connection ID of the client that submitted the query. The connection ID equals the connection ID returned when the client first connects and theIdvalue in the output fromSHOW PROCESSLIST.database: The database name on which the query is being executed.user: The username used to connect to the server.host: The hostname of the client.
query-done: Triggered once the query has been executed and the information has been returned to the client. The probe includes a single argument,status, which returns 0 when the query is successfully executed and 1 if there was an error.
You can get a simple report of the execution time for each query using the following D script:
#!/usr/sbin/dtrace -s
#pragma D option quiet
dtrace:::BEGIN
{
printf("%-20s %-20s %-40s %-9s\n", "Who", "Database", "Query", "Time(ms)");
}
mysql*:::query-start
{
self->query = copyinstr(arg0);
self->connid = arg1;
self->db = copyinstr(arg2);
self->who = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
self->querystart = timestamp;
}
mysql*:::query-done
{
printf("%-20s %-20s %-40s %-9d\n",self->who,self->db,self->query,
(timestamp - self->querystart) / 1000000);
}When executing the above script you should get a basic idea of the execution time of your queries:
shell> ./query.d Who Database Query Time(ms) root@localhost test select * from t1 order by i limit 10 0 root@localhost test set global query_cache_size=0 0 root@localhost test select * from t1 order by i limit 10 776 root@localhost test select * from t1 order by i limit 10 773 root@localhost test select * from t1 order by i desc limit 10 795
The query parsing probes are triggered before the original SQL statement is parsed and when the parsing of the statement and determination of the execution model required to process the statement has been completed:
query-parse-start(query) query-parse-done(status)
query-parse-start: Triggered just before the statement is parsed by the MySQL query parser. The single argument,query, is a string containing the full text of the original query.query-parse-done: Triggered when the parsing of the original statement has been completed. Thestatusis an integer describing the status of the operation. A0indicates that the query was successfully parsed. A1indicates that the parsing of the query failed.
For example, you could monitor the execution time for parsing a given query using the following D script:
#!/usr/sbin/dtrace -s
#pragma D option quiet
mysql*:::query-parse-start
{
self->parsestart = timestamp;
self->parsequery = copyinstr(arg0);
}
mysql*:::query-parse-done
/arg0 == 0/
{
printf("Parsing %s: %d microseconds\n", self->parsequery,((timestamp - self->parsestart)/1000));
}
mysql*:::query-parse-done
/arg0 != 0/
{
printf("Error parsing %s: %d microseconds\n", self->parsequery,((timestamp - self->parsestart)/1000));
}
In the above script a predicate is used on
query-parse-done so that different output is
generated based on the status value of the probe.
When running the script and monitoring the execution:
shell> ./query-parsing.d Error parsing select from t1 join (t2) on (t1.i = t2.i) order by t1.s,t1.i limit 10: 36 ms Parsing select * from t1 join (t2) on (t1.i = t2.i) order by t1.s,t1.i limit 10: 176 ms
The query cache probes are fired when executing any query. The
query-cache-hit query is triggered when a
query exists in the query cache and can be used to return the
query cache information. The arguments contain the original
query text and the number of rows returned from the query cache
for the query. If the query is not within the query cache, or
the query cache is not enabled, then the
query-cache-miss probe is triggered instead.
query-cache-hit(query, rows) query-cache-miss(query)
query-cache-hit: Triggered when the query has been found within the query cache. The first argument,query, contains the original text of the query. The second argument,rows, is an integer containing the number of rows in the cached query.query-cache-miss: Triggered when the query is not found within the query cache. The first argument,query, contains the original text of the query.
The query cache probes are best combined with a probe on the main query so that you can determine the differences in times between using or not using the query cache for specified queries. For example, in the following D script, the query and query cache information are combined into the information output during monitoring:
#!/usr/sbin/dtrace -s
#pragma D option quiet
dtrace:::BEGIN
{
printf("%-20s %-20s %-40s %2s %-9s\n", "Who", "Database", "Query", "QC", "Time(ms)");
}
mysql*:::query-start
{
self->query = copyinstr(arg0);
self->connid = arg1;
self->db = copyinstr(arg2);
self->who = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
self->querystart = timestamp;
self->qc = 0;
}
mysql*:::query-cache-hit
{
self->qc = 1;
}
mysql*:::query-cache-miss
{
self->qc = 0;
}
mysql*:::query-done
{
printf("%-20s %-20s %-40s %-2s %-9d\n",self->who,self->db,self->query,(self->qc ? "Y" : "N"),
(timestamp - self->querystart) / 1000000);
}When executing the script you can see the effects of the query cache. Initially the query cache is disabled. If you set the query cache size and then execute the query multiple times you should see that the query cache is being used to return the query data:
shell> ./query-cache.d root@localhost test select * from t1 order by i limit 10 N 1072 root@localhost set global query_cache_size=262144 N 0 root@localhost test select * from t1 order by i limit 10 N 781 root@localhost test select * from t1 order by i limit 10 Y 0
The query execution probe is triggered when the actual execution of the query starts, after the parsing and checking the query cache but before any privilege checks or optimization. By comparing the difference between the start and done probes you can monitor the time actually spent servicing the query (instead of just handling the parsing and other elements of the query).
query-exec-start(query, connectionid, database, user, host, exec_type) query-exec-done(status)
The information provided in the arguments for
query-start and
query-exec-start are almost identical and
designed so that you can choose to monitor either the entire
query process (using query-start) or only
the execution (using query-exec-start)
while exposing the core information about the user, client,
and query being executed.
query-exec-start: Triggered when the execution of a individual query is started. The arguments are:query: The full text of the submitted query.connectionid: The connection ID of the client that submitted the query. The connection ID equals the connection ID returned when the client first connects and theIdvalue in the output fromSHOW PROCESSLIST.database: The database name on which the query is being executed.user: The username used to connect to the server.host: The hostname of the client.exec_type: The type of execution. Execution types are determined based on the contents of the query and where it was submitted. The values for each type are shown in the following table.Value Description 0 Executed query from sql_parse, top-level query. 1 Executed prepared statement 2 Executed cursor statement 3 Executed query in stored procedure
query-exec-done: Triggered when the execution of the query has completed. The probe includes a single argument,status, which returns 0 when the query is successfully executed and 1 if there was an error.
The *row-{start,done} probes are triggered
each time a row operation is pushed down to a storage engine.
For example, if you execute an
INSERT statement with 100 rows of
data, then the insert-row-start and
insert-row-done probes will be triggered 100
times each, for each row insert.
insert-row-start(database, table) insert-row-done(status) update-row-start(database, table) update-row-done(status) delete-row-start(database, table) delete-row-done(status)
insert-row-start: Triggered before a row is inserted into a table.insert-row-done: Triggered after a row is inserted into a table.update-row-start: Triggered before a row is updated in a table.update-row-done: Triggered before a row is updated in a table.delete-row-start: Triggered before a row is deleted from a table.delete-row-done: Triggered before a row is deleted from a table.
The arguments supported by the probes are consistent for the
corresponding start and
done probes in each case:
database: The database name.table: The table name.status: The status; 0 for success or 1 for failure.
Because the row-level probes are triggered for each individual
row access, these probes can be triggered many thousands of
times each second, which may have a detrimental effect on both
the monitoring script and MySQL. The DTrace environment should
limit the triggering on these probes to prevent the performance
being adversely affected. Either use the probes sparingly, or
use counter or aggregation functions to report on these probes
and then provide a summary when the script terminates or as part
of a query-done or
query-exec-done probes.
The following example script summarizes the duration of each row operation within a larger query:
#!/usr/sbin/dtrace -s
#pragma D option quiet
dtrace:::BEGIN
{
printf("%-2s %-10s %-10s %9s %9s %-s \n",
"St", "Who", "DB", "ConnID", "Dur ms", "Query");
}
mysql*:::query-start
{
self->query = copyinstr(arg0);
self->who = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
self->db = copyinstr(arg2);
self->connid = arg1;
self->querystart = timestamp;
self->rowdur = 0;
}
mysql*:::query-done
{
this->elapsed = (timestamp - self->querystart) /1000000;
printf("%2d %-10s %-10s %9d %9d %s\n",
arg0, self->who, self->db,
self->connid, this->elapsed, self->query);
}
mysql*:::query-done
/ self->rowdur /
{
printf("%34s %9d %s\n", "", (self->rowdur/1000000), "-> Row ops");
}
mysql*:::insert-row-start
{
self->rowstart = timestamp;
}
mysql*:::delete-row-start
{
self->rowstart = timestamp;
}
mysql*:::update-row-start
{
self->rowstart = timestamp;
}
mysql*:::insert-row-done
{
self->rowdur += (timestamp-self->rowstart);
}
mysql*:::delete-row-done
{
self->rowdur += (timestamp-self->rowstart);
}
mysql*:::update-row-done
{
self->rowdur += (timestamp-self->rowstart);
}
Running the above script with a query that inserts data into a table, you can monitor the exact time spent performing the raw row insertion:
St Who DB ConnID Dur ms Query
0 @localhost test 13 20767 insert into t1(select * from t2)
4827 -> Row ops
The read row probes are triggered at a storage engine level each
time a row read operation occurs. These probes are specified
within each storage engine (as opposed to the
*row-start probes which are in the storage
engine interface). These probes can therefore be used to monitor
individual storage engine row-level operations and performance.
Because these probes are triggered around the storage engine row
read interface, they may be hit a significant number of times
during a basic query.
read-row-start(database, table, scan_flag) read-row-done(status)
read-row-start: Triggered when a row is read by the storage engine from the specifieddatabaseandtable. Thescan_flagis set to 1 (true) when the read is part of a table scan (that is, a sequential read), or 0 (false) when the read is of a specific record.read-row-done: Triggered when a row read operation within a storage engine completes. Thestatusreturns 0 on success, or a positive value on failure.
The index probes are triggered each time a row is read using one of the indexes for the specified table. The probe is triggered within the corresponding storage engine for the table.
index-read-row-start(database, table) index-read-row-done(status)
index-read-row-start: Triggered when a row is read by the storage engine from the specifieddatabaseandtable.index-read-row-done: Triggered when an indexed row read operation within a storage engine completes. Thestatusreturns 0 on success, or a positive value on failure.
The lock probes are called whenever an external lock is requested by MySQL for a table using the corresponding lock mechanism on the table as defined by the table's engine type. There are three different types of lock, the read lock, write lock, and unlock operations. Using the probes you can determine the duration of the external locking routine (that is, the time taken by the storage engine to implement the lock, including any time waiting for another lock to become free) and the total duration of the lock/unlock process.
handler-rdlock-start(database, table) handler-rdlock-done(status) handler-wrlock-start(database, table) handler-wrlock-done(status) handler-unlock-start(database, table) handler-unlock-done(status)
handler-rdlock-start: Triggered when a read lock is requested on the specifieddatabaseandtable.handler-wrlock-start: Triggered when a write lock is requested on the specifieddatabaseandtable.handler-unlock-start: Triggered when an unlock request is made on the specifieddatabaseandtable.handler-rdlock-done: Triggered when a read lock request completes. Thestatusis 0 if the lock operation succeeded, or>0on failure.handler-wrlock-done: Triggered when a write lock request completes. Thestatusis 0 if the lock operation succeeded, or>0on failure.handler-unlock-done: Triggered when an unlock request completes. Thestatusis 0 if the unlock operation succeeded, or>0on failure.
You can use arrays to monitor the locking and unlocking of individual tables and then calculate the duration of the entire table lock using the following script:
#!/usr/sbin/dtrace -s
#pragma D option quiet
mysql*:::handler-rdlock-start
{
self->rdlockstart = timestamp;
this->lockref = strjoin(copyinstr(arg0),strjoin("@",copyinstr(arg1)));
self->lockmap[this->lockref] = self->rdlockstart;
printf("Start: Lock->Read %s.%s\n",copyinstr(arg0),copyinstr(arg1));
}
mysql*:::handler-wrlock-start
{
self->wrlockstart = timestamp;
this->lockref = strjoin(copyinstr(arg0),strjoin("@",copyinstr(arg1)));
self->lockmap[this->lockref] = self->rdlockstart;
printf("Start: Lock->Write %s.%s\n",copyinstr(arg0),copyinstr(arg1));
}
mysql*:::handler-unlock-start
{
self->unlockstart = timestamp;
this->lockref = strjoin(copyinstr(arg0),strjoin("@",copyinstr(arg1)));
printf("Start: Lock->Unlock %s.%s (%d ms lock duration)\n",
copyinstr(arg0),copyinstr(arg1),
(timestamp - self->lockmap[this->lockref])/1000000);
}
mysql*:::handler-rdlock-done
{
printf("End: Lock->Read %d ms\n",
(timestamp - self->rdlockstart)/1000000);
}
mysql*:::handler-wrlock-done
{
printf("End: Lock->Write %d ms\n",
(timestamp - self->wrlockstart)/1000000);
}
mysql*:::handler-unlock-done
{
printf("End: Lock->Unlock %d ms\n",
(timestamp - self->unlockstart)/1000000);
}
When executed, you should get information both about the duration of the locking process itself, and of the locks on a specific table:
Start: Lock->Read test.t2 End: Lock->Read 0 ms Start: Lock->Unlock test.t2 (25743 ms lock duration) End: Lock->Unlock 0 ms Start: Lock->Read test.t2 End: Lock->Read 0 ms Start: Lock->Unlock test.t2 (1 ms lock duration) End: Lock->Unlock 0 ms Start: Lock->Read test.t2 End: Lock->Read 0 ms Start: Lock->Unlock test.t2 (1 ms lock duration) End: Lock->Unlock 0 ms Start: Lock->Read test.t2 End: Lock->Read 0 ms
The filesort probes are triggered whenever a filesort operation is applied to a table. For more information on filesort and the conditions under which it occurs, see Section 9.2.1.15, “ORDER BY Optimization”.
filesort-start(database, table) filesort-done(status, rows)
filesort-start: Triggered when the filesort operation starts on a table. The two arguments to the probe,databaseandtable, will identify the table being sorted.filesort-done: Triggered when the filesort operation completes. Two arguments are supplied, thestatus(0 for success, 1 for failure), and the number of rows sorted during the filesort process.
An example of this is in the following script, which tracks the duration of the filesort process in addition to the duration of the main query:
#!/usr/sbin/dtrace -s
#pragma D option quiet
dtrace:::BEGIN
{
printf("%-2s %-10s %-10s %9s %18s %-s \n",
"St", "Who", "DB", "ConnID", "Dur microsec", "Query");
}
mysql*:::query-start
{
self->query = copyinstr(arg0);
self->who = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
self->db = copyinstr(arg2);
self->connid = arg1;
self->querystart = timestamp;
self->filesort = 0;
self->fsdb = "";
self->fstable = "";
}
mysql*:::filesort-start
{
self->filesort = timestamp;
self->fsdb = copyinstr(arg0);
self->fstable = copyinstr(arg1);
}
mysql*:::filesort-done
{
this->elapsed = (timestamp - self->filesort) /1000;
printf("%2d %-10s %-10s %9d %18d Filesort on %s\n",
arg0, self->who, self->fsdb,
self->connid, this->elapsed, self->fstable);
}
mysql*:::query-done
{
this->elapsed = (timestamp - self->querystart) /1000;
printf("%2d %-10s %-10s %9d %18d %s\n",
arg0, self->who, self->db,
self->connid, this->elapsed, self->query);
}
Executing a query on a large table with an ORDER
BY clause that triggers a filesort, and then creating
an index on the table and then repeating the same query, you can
see the difference in execution speed:
St Who DB ConnID Dur microsec Query 0 @localhost test 14 11335469 Filesort on t1 0 @localhost test 14 11335787 select * from t1 order by i limit 100 0 @localhost test 14 466734378 create index t1a on t1 (i) 0 @localhost test 14 26472 select * from t1 order by i limit 100
The individual statement probes are provided to give specific
information about different statement types. For the start
probes the string of the query is provided as the only argument.
Depending on the statement type, the information provided by the
corresponding done probe will differ. For all done probes the
status of the operation (0 for success,
>0 for failure) is provided. For
SELECT,
INSERT,
INSERT ... (SELECT FROM
...), DELETE, and
DELETE FROM
t1,t2 operations the number of rows affected is
returned.
For UPDATE and
UPDATE t1,t2
... statements the number of rows matched and the
number of rows actually changed is provided. This is because the
number of rows actually matched by the corresponding
WHERE clause, and the number of rows changed
can differ. MySQL does not update the value of a row if the
value already matches the new setting.
select-start(query) select-done(status,rows) insert-start(query) insert-done(status,rows) insert-select-start(query) insert-select-done(status,rows) update-start(query) update-done(status,rowsmatched,rowschanged) multi-update-start(query) multi-update-done(status,rowsmatched,rowschanged) delete-start(query) delete-done(status,rows) multi-delete-start(query) multi-delete-done(status,rows)
select-start: Triggered before aSELECTstatement.select-done: Triggered at the end of aSELECTstatement.insert-start: Triggered before aINSERTstatement.insert-done: Triggered at the end of anINSERTstatement.insert-select-start: Triggered before anINSERT ... SELECTstatement.insert-select-done: Triggered at the end of anINSERT ... SELECTstatement.update-start: Triggered before anUPDATEstatement.update-done: Triggered at the end of anUPDATEstatement.multi-update-start: Triggered before anUPDATEstatement involving multiple tables.multi-update-done: Triggered at the end of anUPDATEstatement involving multiple tables.delete-start: Triggered before aDELETEstatement.delete-done: Triggered at the end of aDELETEstatement.multi-delete-start: Triggered before aDELETEstatement involving multiple tables.multi-delete-done: Triggered at the end of aDELETEstatement involving multiple tables.
The arguments for the statement probes are:
query: The query string.status: The status of the query.0for success, and>0for failure.rows: The number of rows affected by the statement. This returns the number rows found forSELECT, the number of rows deleted forDELETE, and the number of rows successfully inserted forINSERT.rowsmatched: The number of rows matched by theWHEREclause of anUPDATEoperation.rowschanged: The number of rows actually changed during anUPDATEoperation.
You use these probes to monitor the execution of these statement types without having to monitor the user or client executing the statements. A simple example of this is to track the execution times:
#!/usr/sbin/dtrace -s
#pragma D option quiet
dtrace:::BEGIN
{
printf("%-60s %-8s %-8s %-8s\n", "Query", "RowsU", "RowsM", "Dur (ms)");
}
mysql*:::update-start, mysql*:::insert-start,
mysql*:::delete-start, mysql*:::multi-delete-start,
mysql*:::multi-delete-done, mysql*:::select-start,
mysql*:::insert-select-start, mysql*:::multi-update-start
{
self->query = copyinstr(arg0);
self->querystart = timestamp;
}
mysql*:::insert-done, mysql*:::select-done,
mysql*:::delete-done, mysql*:::multi-delete-done, mysql*:::insert-select-done
/ self->querystart /
{
this->elapsed = ((timestamp - self->querystart)/1000000);
printf("%-60s %-8d %-8d %d\n",
self->query,
0,
arg1,
this->elapsed);
self->querystart = 0;
}
mysql*:::update-done, mysql*:::multi-update-done
/ self->querystart /
{
this->elapsed = ((timestamp - self->querystart)/1000000);
printf("%-60s %-8d %-8d %d\n",
self->query,
arg1,
arg2,
this->elapsed);
self->querystart = 0;
}When executed you can see the basic execution times and rows matches:
Query RowsU RowsM Dur (ms) select * from t2 0 275 0 insert into t2 (select * from t2) 0 275 9 update t2 set i=5 where i > 75 110 110 8 update t2 set i=5 where i < 25 254 134 12 delete from t2 where i < 5 0 0 0
Another alternative is to use the aggregation functions in DTrace to aggregate the execution time of individual statements together:
#!/usr/sbin/dtrace -s
#pragma D option quiet
mysql*:::update-start, mysql*:::insert-start,
mysql*:::delete-start, mysql*:::multi-delete-start,
mysql*:::multi-delete-done, mysql*:::select-start,
mysql*:::insert-select-start, mysql*:::multi-update-start
{
self->querystart = timestamp;
}
mysql*:::select-done
{
@statements["select"] = sum(((timestamp - self->querystart)/1000000));
}
mysql*:::insert-done, mysql*:::insert-select-done
{
@statements["insert"] = sum(((timestamp - self->querystart)/1000000));
}
mysql*:::update-done, mysql*:::multi-update-done
{
@statements["update"] = sum(((timestamp - self->querystart)/1000000));
}
mysql*:::delete-done, mysql*:::multi-delete-done
{
@statements["delete"] = sum(((timestamp - self->querystart)/1000000));
}
tick-30s
{
printa(@statements);
}
The script just shown aggregates the times spent doing each operation, which could be used to help benchmark a standard suite of tests.
delete 0 update 0 insert 23 select 2484 delete 0 update 0 insert 39 select 10744 delete 0 update 26 insert 56 select 10944 delete 0 update 26 insert 2287 select 15985
The network probes monitor the transfer of information from the MySQL server and clients of all types over the network. The probes are defined as follows:
net-read-start() net-read-done(status, bytes) net-write-start(bytes) net-write-done(status)
net-read-start: Triggered when a network read operation is started.net-read-done: Triggered when the network read operation completes. Thestatusis anintegerrepresenting the return status for the operation,0for success and1for failure. Thebytesargument is an integer specifying the number of bytes read during the process.net-start-bytes: Triggered when data is written to a network socket. The single argument,bytes, specifies the number of bytes written to the network socket.net-write-done: Triggered when the network write operation has completed. The single argument,status, is an integer representing the return status for the operation,0for success and1for failure.
You can use the network probes to monitor the time spent reading
from and writing to network clients during execution. The
following D script provides an example of this. Both the
cumulative time for the read or write is calculated, and the
number of bytes. Note that the dynamic variable size has been
increased (using the dynvarsize option) to
cope with the rapid firing of the individual probes for the
network reads/writes.
#!/usr/sbin/dtrace -s
#pragma D option quiet
#pragma D option dynvarsize=4m
dtrace:::BEGIN
{
printf("%-2s %-30s %-10s %9s %18s %-s \n",
"St", "Who", "DB", "ConnID", "Dur microsec", "Query");
}
mysql*:::query-start
{
self->query = copyinstr(arg0);
self->who = strjoin(copyinstr(arg3),strjoin("@",copyinstr(arg4)));
self->db = copyinstr(arg2);
self->connid = arg1;
self->querystart = timestamp;
self->netwrite = 0;
self->netwritecum = 0;
self->netwritebase = 0;
self->netread = 0;
self->netreadcum = 0;
self->netreadbase = 0;
}
mysql*:::net-write-start
{
self->netwrite += arg0;
self->netwritebase = timestamp;
}
mysql*:::net-write-done
{
self->netwritecum += (timestamp - self->netwritebase);
self->netwritebase = 0;
}
mysql*:::net-read-start
{
self->netreadbase = timestamp;
}
mysql*:::net-read-done
{
self->netread += arg1;
self->netreadcum += (timestamp - self->netreadbase);
self->netreadbase = 0;
}
mysql*:::query-done
{
this->elapsed = (timestamp - self->querystart) /1000000;
printf("%2d %-30s %-10s %9d %18d %s\n",
arg0, self->who, self->db,
self->connid, this->elapsed, self->query);
printf("Net read: %d bytes (%d ms) write: %d bytes (%d ms)\n",
self->netread, (self->netreadcum/1000000),
self->netwrite, (self->netwritecum/1000000));
}When executing the above script on a machine with a remote client, you can see that approximately a third of the time spent executing the query is related to writing the query results back to the client.
St Who DB ConnID Dur microsec Query 0 root@::ffff:192.168.0.108 test 31 3495 select * from t1 limit 1000000 Net read: 0 bytes (0 ms) write: 10000075 bytes (1220 ms)
The keycache probes are triggered when using the index key cache used with the MyISAM storage engine. Probes exist to monitor when data is read into the keycache, cached key data is written from the cache into a cached file, or when accessing the keycache.
Keycache usage indicates when data is read or written from the index files into the cache, and can be used to monitor how efficient the memory allocated to the keycache is being used. A high number of keycache reads across a range of queries may indicate that the keycache is too small for size of data being accessed.
keycache-read-start(filepath, bytes, mem_used, mem_free) keycache-read-block(bytes) keycache-read-hit() keycache-read-miss() keycache-read-done(mem_used, mem_free) keycache-write-start(filepath, bytes, mem_used, mem_free) keycache-write-block(bytes) keycache-write-done(mem_used, mem_free)
When reading data from the index files into the keycache, the
process first initializes the read operation (indicated by
keycache-read-start), then loads blocks of
data (keycache-read-block), and then the read
block is either matches the data being identified
(keycache-read-hit) or more data needs to be
read (keycache-read-miss). Once the read
operation has completed, reading stops with the
keycache-read-done.
Data will be read from the index file into the keycache only when the specified key is not already within the keycache.
keycache-read-start: Triggered when the keycache read operation is started. Data is read from the specifiedfilepath, reading the specified number ofbytes. Themem_usedandmem_availindicate memory currently used by the keycache and the amount of memory available within the keycache.keycache-read-block: Triggered when the keycache reads a block of data, of the specified number ofbytes, from the index file into the keycache.keycache-read-hit: Triggered when the block of data read from the index file matches the key data requested.keycache-read-miss: Triggered when the block of data read from the index file does not match the key data needed.keycache-read-done: Triggered when the keycache read operation has completed. Themem_usedandmem_availindicate memory currently used by the keycache and the amount of memory available within the keycache.
Keycache writes occur when the index information is updated
during an INSERT, UPDATE,
or DELETE operation, and the cached key
information is flushed back to the index file.
keycache-write-start: Triggered when the keycache write operation is started. Data is written to the specifiedfilepath, reading the specified number ofbytes. Themem_usedandmem_availindicate memory currently used by the keycache and the amount of memory available within the keycache.keycache-write-block: Triggered when the keycache writes a block of data, of the specified number ofbytes, to the index file from the keycache.keycache-write-done: Triggered when the keycache write operation has completed. Themem_usedandmem_availindicate memory currently used by the keycache and the amount of memory available within the keycache.