casacore
StandardStMan.h
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1//# StandardStMan.h: The Standard Storage Manager
2//# Copyright (C) 2000,2002
3//# Associated Universities, Inc. Washington DC, USA.
4//#
5//# This library is free software; you can redistribute it and/or modify it
6//# under the terms of the GNU Library General Public License as published by
7//# the Free Software Foundation; either version 2 of the License, or (at your
8//# option) any later version.
9//#
10//# This library is distributed in the hope that it will be useful, but WITHOUT
11//# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12//# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
13//# License for more details.
14//#
15//# You should have received a copy of the GNU Library General Public License
16//# along with this library; if not, write to the Free Software Foundation,
17//# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
18//#
19//# Correspondence concerning AIPS++ should be addressed as follows:
20//# Internet email: aips2-request@nrao.edu.
21//# Postal address: AIPS++ Project Office
22//# National Radio Astronomy Observatory
23//# 520 Edgemont Road
24//# Charlottesville, VA 22903-2475 USA
25//#
26//# $Id$
27
28#ifndef TABLES_STANDARDSTMAN_H
29#define TABLES_STANDARDSTMAN_H
30
31//# Includes
32#include <casacore/casa/aips.h>
33#include <casacore/tables/DataMan/SSMBase.h>
34
35
36namespace casacore { //# NAMESPACE CASACORE - BEGIN
37
38// <summary>
39// The Standard Storage Manager
40// </summary>
41
42// <use visibility=export>
43
44// <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="tStandardStMan.cc">
45// </reviewed>
46
47// <prerequisite>
48//# Classes you should understand before using this one.
49// <li> The Table Data Managers concept as described in module file
50// <linkto module="Tables:Data Managers">Tables.h</linkto>
51// <li> <linkto class=ROStandardStManAccessor>
52// ROStandardStManAccessor</linkto>
53// for a discussion of the cache size
54// </prerequisite>
55
56// <etymology>
57// StandardStMan is the data manager which stores the data in a
58// standard way. I.e. it does not use special techniques like
59// other storage managers do.
60// </etymology>
61
62// <synopsis>
63// StandardStMan is meant as the storage manager to be used standardly.
64// Other storage managers like
65// <linkto class=IncrementalStMan>IncrementalStMan</linkto> and the
66// <linkto class=TiledStMan>TiledStMan</linkto> derivatives should
67// only be used when appropriate.
68// <br>
69// Like the other storage managers StandardStMan uses
70// <linkto class=BucketCache>bucket-based</linkto> access to its data.
71// where a bucket contains the number of columns and rows that fit best.
72// Variable length strings are stored in separate buckets because they do
73// not fit in the fixed bucket layout used for the other columns.
74// Only fixed length strings and strings <= 8 characters are stored directly.
75// Note that, in fact, fixed length string means maximum length strings.
76// It can be set using the <src>setMaxLength</src> function in
77// class <linkto class=ColumnDesc>ColumnDesc</linkto> or
78// class <linkto class=BaseColumnDesc>BaseColumnDesc</linkto>.
79// <p>
80// The file size is at least the size of a bucket, even if only the table
81// contains only a few rows, thus uses only a fraction of a bucket.
82// The default bucketsize is 32 rows. This means that if it is known
83// in advance that the table will contain many more rows, it might make
84// sense to construct the StandardStMan with a larger bucketsize.
85// <p>
86// StandardStMan is a robust storage manager. Care has been taken
87// that its index cannot be corrupted in case of exceptions like
88// device full or crash.
89// <p>
90// StandardStMan supports the following functionality:
91// <ol>
92// <li> Removal of rows. This leaves some empty space in a bucket.
93// An empty bucket will be reused.
94// <li> Addition of rows. This is always done in the last bucket
95// and a new bucket is added when needed.
96// <li> Removal of a column. This also leaves empty space, which will
97// be reused when a newly added column fits in it.
98// <li> Addition of a column. If available, empty column space is used.
99// Otherwise it creates as many new buckets as needed.
100// </ol>
101// All direct data (scalars and direct arrays) is stored in the main file.
102// Indirect arrays (except strings) are stored in a second file.
103// Indirect string arrays are also stored in the main file, because in
104// that way frequently rewriting indirect strings arrays wastes far
105// less space.
106// <p>
107// As said above all string arrays and variable length scalar strings
108// are stored in separate string buckets.
109// </synopsis>
110
111// <motivation>
112// StManAipsIO is the standard storage manager used so far.
113// Its major drawback is that it is memory based which makes it
114// not usable for large tables. Furthermore it is not a very robust
115// storage manager. When a system crashes, tables might get corrupted.
116// <br>
117// These drawbacks have been adressed in this new StandardStman.
118// It uses a bucket-based access scheme and makes sure that its
119// indices are stored in a way that they can hardly get corrupted.
120// </motivation>
121
122// <example>
123// The following example shows how to create a table and how to attach
124// the storage manager to some columns.
125// <srcblock>
126// SetupNewTable newtab("name.data", tableDesc, Table::New);
127// StandardStMan stman; // define storage manager
128// newtab.bindColumn ("column1", stman); // bind column to st.man.
129// newtab.bindColumn ("column2", stman); // bind column to st.man.
130// Table tab(newtab); // actually create table
131// </srcblock>
132//
133// The following example shows how to create a StandardStMan storage
134// manager for a table with 16 rows. By giving the (expected) nr of rows
135// to the storage manager, it can optimize its bucket size.
136// <srcblock>
137// SetupNewTable newtab("name.data", tableDesc, Table::New);
138// StandardStMan stman(-16);
139// newtab.bindAll ("column1", stman); // bind all columns to st.man.
140// Table tab(newtab); // actually create table
141// </srcblock>
142// </example>
143
144//# <todo asof="$DATE:$">
145//# A List of bugs, limitations, extensions or planned refinements.
146//# </todo>
147
148
149class StandardStMan : public SSMBase
150{
151public:
152 // Create a Standard storage manager with the given name.
153 // If no name is used, it is set to "SSM"
154 // The name can be used to construct a
155 // <linkto class=ROStandardStManAccessor>ROStandardStManAccessor
156 // </linkto> object (e.g. to set the cache size).
157 // <br>
158 // The cache size has to be given in buckets.
159 // <br>
160 // The bucket size can be given in 2 ways:
161 // <br>- A positive number gives the bucket size in bytes.
162 // The number of rows per bucket will be calculated from it.
163 // <br>- A negative number gives the number of rows per bucket.
164 // The bucket size in bytes will be calculated from it.
165 // Note that in this way the maximum bucketsize is 32768 (minimum is 128).
166 // <br>- The default 0 means that 32 rows will be stored in a bucket.
167 // <br>Note that the default is only suitable for small tables.
168 // In general it makes sense to give the expected number of table rows.
169 // In that way the buckets will be small enough for small tables
170 // and not too small for large tables.
171 // <group>
172 explicit StandardStMan (Int bucketSize = 0,
173 uInt cacheSize = 1);
175 Int bucketSize = 0,
176 uInt cacheSize = 1);
177 // </group>
178
180
181private:
182 // Copy constructor cannot be used.
184
185 // Assignment cannot be used.
187};
188
189
190
191} //# NAMESPACE CASACORE - END
192
193#endif
virtual String dataManagerName() const
Get the name given to the storage manager (in the constructor).
StandardStMan(Int bucketSize=0, uInt cacheSize=1)
Create a Standard storage manager with the given name.
StandardStMan & operator=(const StandardStMan &that)
Assignment cannot be used.
StandardStMan(const StandardStMan &that)
Copy constructor cannot be used.
StandardStMan(const String &dataManagerName, Int bucketSize=0, uInt cacheSize=1)
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
unsigned int uInt
Definition: aipstype.h:51
int Int
Definition: aipstype.h:50