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TSMOption.h
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1//# TSMOption.h: Options for the Tiled Storage Manager Access
2//# Copyright (C) 2010
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 receied 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_TSMOPTION_H
29#define TABLES_TSMOPTION_H
30
31
32//# Includes
33#include <casacore/casa/aips.h>
34
35namespace casacore { //# NAMESPACE CASACORE - BEGIN
36
37// <summary>
38// Options for the Tiled Storage Manager Access
39// </summary>
40
41// <use visibility=export>
42
43// <reviewed reviewer="TPPR" date="08.11.94" tests="tTiledShapeStMan.cc">
44// </reviewed>
45
46// <prerequisite>
47//# Classes you should understand before using this one.
48// <li> <linkto class=TiledStMan>TiledStMan</linkto>
49// </prerequisite>
50
51// <synopsis>
52// This class can be used to define how the Tiled Storage Manager accesses
53// its data. There are three ways:
54// <ol>
55// <li> Using a cache of its own. The cache size is derived using the hinted
56// access pattern. The cache can be (too) large when using large tables
57// with bad access patterns.
58// A maximum cache size can be defined to overcome this problem, but
59// that may result in poor caching behaviour.
60// Until January 2010 this was the only way to access the data.
61// <li> Use memory-mapped IO (mmap); the operating system take care of caching.
62// On 32-bit systems mmap cannot be used for larger tables due to the
63// 4 GB address space limit.
64// When creating or extending files, mmap can be disadvantageous because
65// extending the file requires remapping it.
66// <li> Use buffered IO; the kernel's file cache should avoid unnecessary IO.
67// Its performance is less than mmap, but it works well on 32-bit systems.
68// The buffer size to be used can be defined.
69// </ol>
70//
71// The constructor of the class can be used to define the options or
72// to read options from the aipsrc file.
73// <ul>
74// <li> <src>TSMOption::Cache</src>
75// Use unbuffered file IO with internal TSM caching. This is the old
76// behaviour.
77// The maximum cache size can be given as a constructor argument.
78// <li> <src>TSMOption::MMap</src>
79// Use memory-mapped IO.
80// <li> <src>TSMOption::Buffer</src>
81// Use buffered file IO without.
82// The buffer size can be given as a constructor argument.
83// <li> <src>TSMOption::Default</src>
84// Use default. This is MMap for existing files on 64-bit systems,
85// otherwise Buffer.
86// <li> <src>TSMOption::Aipsrc</src>
87// Use the option as defined in the aipsrc file.
88// </ul>
89// The aipsrc variables are:
90// <ul>
91// <li> <src>table.tsm.option</src> gives the option as the case-insensitive
92// string value:
93// <ul>
94// <li> <src>cache</src> means TSMCache.
95// <li> <src>mmap</src> (or <src>map</src>) means TSMMap.
96// <li> <src>mmapold</src> (or <src>mapold</src>) means TSMMap for existing
97// tables and TSMDefault for new tables.
98// <li> <src>buffer</src> means TSMBuffer.
99// <li> <src>default</src> means TSMDefault.
100// </ul>
101// It defaults to value <src>default</src>.
102// Note that <src>mmapold</src> is almost the same as <src>default</src>.
103// Only on 32-bit systems it is different.
104// <li> <src>table.tsm.maxcachesizemb</src> gives the maximum cache size in
105// MibiByte for option <src>TSMOption::Cache</src>. A value -1 means
106// that the system determines the maximum. A value 0 means unlimited.
107// It defaults to -1.
108// Note it can always be overridden using class ROTiledStManAccessor.
109// <li> <src>table.tsm.buffersize</src> gives the buffer size for option
110// <src>TSMOption::Buffer</src>. A value <=0 means use the default 4096.
111// It defaults to 0.
112// </ul>
113// </synopsis>
114
115
117 {
118 public:
119 // Define the possible options how the TiledStMan accesses its data.
120 enum Option {
121 // Use unbuffered file IO with internal TSM caching.
123 // Use buffered file IO without internal TSM caching.
125 // Use memory-mapped IO.
127 // Use default.
129 // Use as defined in the aipsrc file.
130 Aipsrc
131 };
132
133 // Create an option object.
134 // The parameter values are described in the synopsis.
135 // A size value -2 means reading that size from the aipsrc file.
136 // The buffer size has to be given in bytes.
137 // The maximum cache size has to be given in MibiBytes (1024*1024 bytes).
140
141 // Fill the option in case Aipsrc or Default was given.
142 // It is done as explained in the synopsis.
143 void fillOption (Bool newFile);
144
145 // Get the option.
147 { return itsOption; }
148
149 // Get the buffer size.
151 { return itsBufferSize; }
152
153 // Get the maximum cache size (in MibiByte). -1 means undefined.
155 { return itsMaxCacheSize; }
156
157 private:
161 };
162
163} //# NAMESPACE CASACORE - END
164
165#endif
Int bufferSize() const
Get the buffer size.
Definition TSMOption.h:150
Option option() const
Get the option.
Definition TSMOption.h:146
TSMOption(Option option=Aipsrc, Int bufferSize=-2, Int maxCacheSizeMB=-2)
Create an option object.
Int maxCacheSizeMB() const
Get the maximum cache size (in MibiByte).
Definition TSMOption.h:154
void fillOption(Bool newFile)
Fill the option in case Aipsrc or Default was given.
Option
Define the possible options how the TiledStMan accesses its data.
Definition TSMOption.h:120
@ Default
Use default.
Definition TSMOption.h:128
@ MMap
Use memory-mapped IO.
Definition TSMOption.h:126
@ Buffer
Use buffered file IO without internal TSM caching.
Definition TSMOption.h:124
@ Cache
Use unbuffered file IO with internal TSM caching.
Definition TSMOption.h:122
this file contains all the compiler specific defines
Definition mainpage.dox:28
int Int
Definition aipstype.h:50
bool Bool
Define the standard types used by Casacore.
Definition aipstype.h:42