casacore
TiledStManAccessor.h
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1 //# TiledStManAccessor.h: Gives access to some TiledStMan functions
2 //# Copyright (C) 1994,1995,1996,1997,1999,2000,2001
3 //# Associated Universities, Inc. Washington DC, USA.
4 //#
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8 //# option) any later version.
9 //#
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13 //# License for more details.
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25 //#
26 //# $Id$
27 
28 #ifndef TABLES_TILEDSTMANACCESSOR_H
29 #define TABLES_TILEDSTMANACCESSOR_H
30 
31 //# Includes
32 #include <casacore/casa/aips.h>
33 #include <casacore/tables/DataMan/DataManAccessor.h>
34 #include <casacore/casa/iosfwd.h>
35 
36 namespace casacore { //# NAMESPACE CASACORE - BEGIN
37 
38 //# Forward Declarations
39 class TiledStMan;
40 class DataManager;
41 class Table;
42 class IPosition;
43 class String;
44 class Record;
45 
46 // <summary>
47 // Give access to some TiledStMan functions
48 // </summary>
49 
50 // <use visibility=local>
51 
52 // <reviewed reviewer="Gareth Hunt" date="94Nov17" tests="">
53 // </reviewed>
54 
55 // <prerequisite>
56 //# Classes you should understand before using this one.
57 // <li> <linkto class=TiledStMan>TiledStMan</linkto>
58 // </prerequisite>
59 
60 // <synopsis>
61 // The Table system has one or more storage managers underneath.
62 // These storage managers are invisible and there is no way to
63 // get access to them.
64 // However, the <linkto class=TiledStMan>TiledStMan</linkto>-type
65 // storage managers are quite specific.
66 // This class ROTiledStManAccessor gives the user the means to
67 // access a TiledStMan-type object and to control it in some way.
68 // <p>
69 // The actions that can be performed deal with the caches used in
70 // a tiled storage manager. Per hypercube a cache is used to keep as many
71 // tiles in memory as needed for efficient access to the data.
72 // The cache size needed is calculated automatically. However,
73 // it may be possible that a cache uses too much memory. Therefore
74 // a maximum cache size can be specified, which can be done in 2 ways:
75 // <ol>
76 // <li> To the constructor of a tiled storage manager. This is
77 // persistent and acts as the default maximum cache size.
78 // <li> Using the function setMaximumCacheSize in this accessor class.
79 // This is not persistent and acts as a temporary overwrite
80 // of the default maximum cache size.
81 // </ol>
82 // It is recommended to set the maximum cache size only when the
83 // tiled storage manager may use too much memory. Setting a
84 // maximum could have the effect that the optimal number of tiles
85 // does not fit in memory leading to excessive read/write activity.
86 // <br>For example:<br>
87 // A hypercube has shape [12,20,30,42] and tile shape [4,5,6,7].
88 // The hypercube contains doubles, so the tilesize is 6720 bytes.
89 // The number of tiles per dimension is [3,4,5,6] resulting in 360 tiles.
90 // Iterating through that hypercube requires that some tiles are kept in
91 // memory to avoid too many read operations. When iterating like
92 // <srcblock>
93 // for (uInt i3=0; i3<42; i3++)
94 // for (uInt i2=0; i2<30; i2++)
95 // for (uInt i1=0; i1<20; i1++)
96 // for (uInt i0=0; i0<12; i0++)
97 // do something with data[i0,i1,i2,i3]
98 // </srcblock>
99 // it is clear that it is best to have a cache which can contain at least
100 // 3*4*5 tiles. In that way each tile is read only once resulting in
101 // 360 reads.
102 // <br>When the cache can hold 3*4 tiles, the first tiles of the 3rd
103 // dimension have been flushed out when the second step in the 4th dimension
104 // gets executed. So the tiles have to be reread for each step in the 4th
105 // dimension, resulting in 3*4*5*42 = 2520 reads.
106 // <br>When the cache can hold only one tile, the situation is dramatic.
107 // A tile has to be read for every 4 pixels, resulting in 75600 reads.
108 // <p>
109 // Apart from setting the maximum cache size, one can also clear the
110 // caches. This can be useful to free memory when an iteration through the
111 // data in the tiled storage manager has been done completely. Clearing
112 // the caches also clears their statistics (see below).
113 // <p>
114 // Showing the statistics of the caches used by a tiled storage
115 // manager is possible. Per cache it shows the number of tiles accessed and
116 // the number of tiles actually read, written, or initialized. The hit ratio
117 // gives a good idea of the cache behaviour.
118 // <p>
119 // Note that the maximum cache size is not an absolute maximum.
120 // When the optimal number of tiles do not fit, it is tried if they fit
121 // when using an overdrawn of maximum 10%. If so, it uses that overdrawn.
122 // If not, it uses the maximum cache size.
123 // <p>
124 // A few functions exist to get information about a hypercube.
125 // The 'get' functions get the information for the given hypercube,
126 // while similar functions without the 'get' prefix do the same for the
127 // given row.
128 // </synopsis>
129 
130 // <motivation>
131 // In principle a pointer to TiledStMan could be used.
132 // However, that would give access to all public functions.
133 // Furthermore it could not distinguish between read/write and readonly
134 // tables.
135 // </motivation>
136 
137 // <example>
138 // This example shows how to set the maximum cache size for
139 // the tiled storage manager with the name "TSMExample". The cache
140 // size is not persistent, i.e. when the same table is reopened
141 // at a later time, this cache size is not remembered.
142 // <srcblock>
143 // // Open a table.
144 // Table table("someName.data");
145 // // Set the maximum cache size of its tiled hypercube storage
146 // // manager TSMExample to 0.5 MiB.
147 // ROTiledStManAccessor accessor(table, "TSMExample");
148 // accessor.setMaximumCacheSize (512*1024);
149 // </srcblock>
150 // </example>
151 
152 //# <todo asof="$DATE:$">
153 //# </todo>
154 
155 
157 {
158 public:
159  // Default constructor should be used with care.
160  // The resulting object cannot be used for any other operation
161  // until a 'true' ROTiledStManAccessor object is assigned to it.
163 
164  // Construct the object for a data manager in the table given the name
165  // of the data manager or the column.
166  // An exception is thrown if the data manager type is not any tiled
167  // storage manager.
168  ROTiledStManAccessor (const Table& table, const String& name,
169  Bool byColumn=False);
170 
172 
173  // Copy constructor (reference semantics).
175 
176  // Assignment (reference semantics).
178 
179  // Set the maximum cache size (in MibiByte) to be used by a hypercube
180  // in the storage manager. Note that each hypercube has its own cache.
181  // 0 means unlimited.
182  // The initial maximum cache size is unlimited.
183  // The maximum cache size given in this way is not persistent.
184  // Only the maximum cache size given to the constructors of the tiled
185  // storage managers, is persistent.
187 
188  // Get the maximum cache size (in MiB).
190 
191  // Get the current cache size (in buckets) for the hypercube in
192  // the given row.
193  uInt cacheSize (rownr_t rownr) const;
194 
195  // Get the hypercube shape of the data in the given row.
196  const IPosition& hypercubeShape (rownr_t rownr) const;
197 
198  // Get the tile shape of the data in the given row.
199  const IPosition& tileShape (rownr_t rownr) const;
200 
201  // Get the bucket size (in bytes) of the hypercube in the given row.
202  uInt bucketSize (rownr_t rownr) const;
203 
204  // Get coordinate and id values of the hypercube in the given row.
205  const Record& valueRecord (rownr_t rownr) const;
206 
207  // Return the number of hypercubes.
208  uInt nhypercubes() const;
209 
210  // Get the current cache size (in buckets) for the given hypercube.
211  uInt getCacheSize (uInt hypercube) const;
212 
213  // Get the shape of the given hypercube.
214  const IPosition& getHypercubeShape (uInt hypercube) const;
215 
216  // Get the tile shape of the given hypercube.
217  const IPosition& getTileShape (uInt hypercube) const;
218 
219  // Get the bucket size (in bytes) of the given hypercube.
220  uInt getBucketSize (uInt hypercube) const;
221 
222  // Get coordinate and id values of the given hypercube.
223  const Record& getValueRecord (uInt hypercube) const;
224 
225  // Calculate the cache size (in buckets) for accessing the hypercube
226  // containing the given row. It takes the maximum cache size into
227  // account (allowing an overdraft of 10%).
228  // It uses the given axisPath (i.e. traversal order) to determine
229  // the optimum size. A window can be specified to indicate that only
230  // the given subset of the hypercube will be accessed. The window
231  // defaults to the entire hypercube.
232  // <br>
233  // The length of the slice and window arguments and <src>axisPath</src>
234  // must be less or equal to the dimensionality of the hypercube.
235  // The non-specified <src>windowStart</src> parts default to 0.
236  // The non-specified <src>windowLength</src> parts default to
237  // the hypercube shape.
238  // The non-specified <src>sliceShape</src> parts default to 1.
239  // <br>
240  // Axispath = [2,0,1] indicates that the z-axis changes most rapidly,
241  // thereafter x and y. An axis can occur only once in the axisPath.
242  // The non-specified <src>axisPath</src> parts get the natural order.
243  // E.g. in the previous example axisPath=[2] defines the same path.
244  // <group>
245  uInt calcCacheSize (rownr_t rownr, const IPosition& sliceShape,
246  const IPosition& axisPath) const;
247  uInt calcCacheSize (rownr_t rownr, const IPosition& sliceShape,
248  const IPosition& windowStart,
249  const IPosition& windowLength,
250  const IPosition& axisPath) const;
251  // </group>
252 
253  // Set the cache size using the corresponding <src>calcCacheSize</src>
254  // function mentioned above.
255  // <br>When forceSmaller is False, the cache is not resized when the
256  // new size is smaller.
257  // <group>
258  void setCacheSize (rownr_t rownr, const IPosition& sliceShape,
259  const IPosition& axisPath,
260  Bool forceSmaller = True);
261  void setCacheSize (rownr_t rownr, const IPosition& sliceShape,
262  const IPosition& windowStart,
263  const IPosition& windowLength,
264  const IPosition& axisPath,
265  Bool forceSmaller = True);
266  // </group>
267 
268  // Set the cache size for accessing the hypercube containing the given row.
269  // When the give cache size exceeds the maximum cache size with more
270  // than 10%, the maximum cache size is used instead.
271  // <br>When forceSmaller is False, the cache is not resized when the
272  // new size is smaller.
273  void setCacheSize (rownr_t rownr, uInt nbuckets, Bool forceSmaller = True);
274 
275  // This version allows setting the tile cache for a particular hypercube. This
276  // is useful when iterating over the hypercubes in an StMan.
277  void setHypercubeCacheSize (uInt hypercube, uInt nbuckets, Bool forceSmaller = True);
278 
279  // Clear the caches used by the hypercubes in this storage manager.
280  // It will flush the caches as needed and remove all buckets from them
281  // resulting in a possibly large drop in memory used.
282  void clearCaches();
283 
284 
285 protected:
286  // Get the data manager.
288 
289 
290 private:
291  //# Declare the data members.
293 };
294 
295 
296 
297 
298 } //# NAMESPACE CASACORE - END
299 
300 #endif
Abstract base class for a data manager.
Definition: DataManager.h:221
ROTiledStManAccessor(const Table &table, const String &name, Bool byColumn=False)
Construct the object for a data manager in the table given the name of the data manager or the column...
void setCacheSize(rownr_t rownr, const IPosition &sliceShape, const IPosition &axisPath, Bool forceSmaller=True)
Set the cache size using the corresponding calcCacheSize function mentioned above.
void clearCaches()
Clear the caches used by the hypercubes in this storage manager.
void setCacheSize(rownr_t rownr, const IPosition &sliceShape, const IPosition &windowStart, const IPosition &windowLength, const IPosition &axisPath, Bool forceSmaller=True)
void setHypercubeCacheSize(uInt hypercube, uInt nbuckets, Bool forceSmaller=True)
This version allows setting the tile cache for a particular hypercube.
const IPosition & hypercubeShape(rownr_t rownr) const
Get the hypercube shape of the data in the given row.
DataManager * getDataManager() const
Get the data manager.
void setMaximumCacheSize(uInt nMiB)
Set the maximum cache size (in MibiByte) to be used by a hypercube in the storage manager.
uInt getBucketSize(uInt hypercube) const
Get the bucket size (in bytes) of the given hypercube.
const IPosition & getTileShape(uInt hypercube) const
Get the tile shape of the given hypercube.
ROTiledStManAccessor(const ROTiledStManAccessor &that)
Copy constructor (reference semantics).
uInt maximumCacheSize() const
Get the maximum cache size (in MiB).
const IPosition & getHypercubeShape(uInt hypercube) const
Get the shape of the given hypercube.
uInt bucketSize(rownr_t rownr) const
Get the bucket size (in bytes) of the hypercube in the given row.
uInt getCacheSize(uInt hypercube) const
Get the current cache size (in buckets) for the given hypercube.
uInt calcCacheSize(rownr_t rownr, const IPosition &sliceShape, const IPosition &axisPath) const
Calculate the cache size (in buckets) for accessing the hypercube containing the given row.
void setCacheSize(rownr_t rownr, uInt nbuckets, Bool forceSmaller=True)
Set the cache size for accessing the hypercube containing the given row.
const Record & getValueRecord(uInt hypercube) const
Get coordinate and id values of the given hypercube.
const IPosition & tileShape(rownr_t rownr) const
Get the tile shape of the data in the given row.
uInt cacheSize(rownr_t rownr) const
Get the current cache size (in buckets) for the hypercube in the given row.
const Record & valueRecord(rownr_t rownr) const
Get coordinate and id values of the hypercube in the given row.
uInt nhypercubes() const
Return the number of hypercubes.
ROTiledStManAccessor & operator=(const ROTiledStManAccessor &that)
Assignment (reference semantics).
ROTiledStManAccessor()
Default constructor should be used with care.
uInt calcCacheSize(rownr_t rownr, const IPosition &sliceShape, const IPosition &windowStart, const IPosition &windowLength, const IPosition &axisPath) const
String: the storage and methods of handling collections of characters.
Definition: String.h:225
this file contains all the compiler specific defines
Definition: mainpage.dox:28
const Bool False
Definition: aipstype.h:44
unsigned int uInt
Definition: aipstype.h:51
bool Bool
Define the standard types used by Casacore.
Definition: aipstype.h:42
const Bool True
Definition: aipstype.h:43
uInt64 rownr_t
Define the type of a row number in a table.
Definition: aipsxtype.h:46