Loading...
Searching...
No Matches
StandardStMan.h
Go to the documentation of this file.
//# StandardStMan.h: The Standard Storage Manager
//# Copyright (C) 2000,2002
//# Associated Universities, Inc. Washington DC, USA.
//#
//# This library is free software; you can redistribute it and/or modify it
//# under the terms of the GNU Library General Public License as published by
//# the Free Software Foundation; either version 2 of the License, or (at your
//# option) any later version.
//#
//# This library is distributed in the hope that it will be useful, but WITHOUT
//# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
//# FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
//# License for more details.
//#
//# You should have received a copy of the GNU Library General Public License
//# along with this library; if not, write to the Free Software Foundation,
//# Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
//#
//# Correspondence concerning AIPS++ should be addressed as follows:
//# Internet email: casa-feedback@nrao.edu.
//# Postal address: AIPS++ Project Office
//# National Radio Astronomy Observatory
//# 520 Edgemont Road
//# Charlottesville, VA 22903-2475 USA
#ifndef TABLES_STANDARDSTMAN_H
#define TABLES_STANDARDSTMAN_H
//# Includes
#include <casacore/casa/aips.h>
#include <casacore/tables/DataMan/SSMBase.h>
namespace casacore { //# NAMESPACE CASACORE - BEGIN
// <summary>
// The Standard Storage Manager
// </summary>
// <use visibility=export>
// <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="tStandardStMan.cc">
// </reviewed>
// <prerequisite>
//# Classes you should understand before using this one.
// <li> The Table Data Managers concept as described in module file
// <linkto module="Tables:Data Managers">Tables.h</linkto>
// <li> <linkto class=ROStandardStManAccessor>
// ROStandardStManAccessor</linkto>
// for a discussion of the cache size
// </prerequisite>
// <etymology>
// StandardStMan is the data manager which stores the data in a
// standard way. I.e. it does not use special techniques like
// other storage managers do.
// </etymology>
// <synopsis>
// StandardStMan is meant as the storage manager to be used standardly.
// Other storage managers like
// <linkto class=IncrementalStMan>IncrementalStMan</linkto> and the
// <linkto class=TiledStMan>TiledStMan</linkto> derivatives should
// only be used when appropriate.
// <br>
// Like the other storage managers StandardStMan uses
// <linkto class=BucketCache>bucket-based</linkto> access to its data.
// where a bucket contains the number of columns and rows that fit best.
// Variable length strings are stored in separate buckets because they do
// not fit in the fixed bucket layout used for the other columns.
// Only fixed length strings and strings <= 8 characters are stored directly.
// Note that, in fact, fixed length string means maximum length strings.
// It can be set using the <src>setMaxLength</src> function in
// class <linkto class=ColumnDesc>ColumnDesc</linkto> or
// class <linkto class=BaseColumnDesc>BaseColumnDesc</linkto>.
// <p>
// The file size is at least the size of a bucket, even if only the table
// contains only a few rows, thus uses only a fraction of a bucket.
// The default bucketsize is 32 rows. This means that if it is known
// in advance that the table will contain many more rows, it might make
// sense to construct the StandardStMan with a larger bucketsize.
// <p>
// StandardStMan is a robust storage manager. Care has been taken
// that its index cannot be corrupted in case of exceptions like
// device full or crash.
// <p>
// StandardStMan supports the following functionality:
// <ol>
// <li> Removal of rows. This leaves some empty space in a bucket.
// An empty bucket will be reused.
// <li> Addition of rows. This is always done in the last bucket
// and a new bucket is added when needed.
// <li> Removal of a column. This also leaves empty space, which will
// be reused when a newly added column fits in it.
// <li> Addition of a column. If available, empty column space is used.
// Otherwise it creates as many new buckets as needed.
// </ol>
// All direct data (scalars and direct arrays) is stored in the main file.
// Indirect arrays (except strings) are stored in a second file.
// Indirect string arrays are also stored in the main file, because in
// that way frequently rewriting indirect strings arrays wastes far
// less space.
// <p>
// As said above all string arrays and variable length scalar strings
// are stored in separate string buckets.
// </synopsis>
// <motivation>
// StManAipsIO is the standard storage manager used so far.
// Its major drawback is that it is memory based which makes it
// not usable for large tables. Furthermore it is not a very robust
// storage manager. When a system crashes, tables might get corrupted.
// <br>
// These drawbacks have been adressed in this new StandardStman.
// It uses a bucket-based access scheme and makes sure that its
// indices are stored in a way that they can hardly get corrupted.
// </motivation>
// <example>
// The following example shows how to create a table and how to attach
// the storage manager to some columns.
// <srcblock>
// SetupNewTable newtab("name.data", tableDesc, Table::New);
// StandardStMan stman; // define storage manager
// newtab.bindColumn ("column1", stman); // bind column to st.man.
// newtab.bindColumn ("column2", stman); // bind column to st.man.
// Table tab(newtab); // actually create table
// </srcblock>
//
// The following example shows how to create a StandardStMan storage
// manager for a table with 16 rows. By giving the (expected) nr of rows
// to the storage manager, it can optimize its bucket size.
// <srcblock>
// SetupNewTable newtab("name.data", tableDesc, Table::New);
// StandardStMan stman(-16);
// newtab.bindAll ("column1", stman); // bind all columns to st.man.
// Table tab(newtab); // actually create table
// </srcblock>
// </example>
//# <todo asof="$DATE:$">
//# A List of bugs, limitations, extensions or planned refinements.
//# </todo>
class StandardStMan : public SSMBase
{
public:
// Create a Standard storage manager with the given name.
// If no name is used, it is set to "SSM"
// The name can be used to construct a
// <linkto class=ROStandardStManAccessor>ROStandardStManAccessor
// </linkto> object (e.g. to set the cache size).
// <br>
// The cache size has to be given in buckets.
// <br>
// The bucket size can be given in 2 ways:
// <br>- A positive number gives the bucket size in bytes.
// The number of rows per bucket will be calculated from it.
// <br>- A negative number gives the number of rows per bucket.
// The bucket size in bytes will be calculated from it.
// Note that in this way the maximum bucketsize is 32768 (minimum is 128).
// <br>- The default 0 means that 32 rows will be stored in a bucket.
// <br>Note that the default is only suitable for small tables.
// In general it makes sense to give the expected number of table rows.
// In that way the buckets will be small enough for small tables
// and not too small for large tables.
// <group>
explicit StandardStMan (Int bucketSize = 0,
uInt cacheSize = 1);
explicit StandardStMan (const String& dataManagerName,
Int bucketSize = 0,
uInt cacheSize = 1);
// </group>
~StandardStMan();
// Copy constructor cannot be used.
StandardStMan (const StandardStMan&) = delete;
// Assignment cannot be used.
StandardStMan& operator= (const StandardStMan&) = delete;
};
} //# NAMESPACE CASACORE - END
#endif
casacore::SSMBase::SSMBase
SSMBase(Int aBucketSize=0, uInt aCacheSize=1)
Create a Standard storage manager with default name SSM.
casacore::SSMBase::dataManagerName
virtual String dataManagerName() const
Get the name given to the storage manager (in the constructor).
casacore::StandardStMan::StandardStMan
StandardStMan(Int bucketSize=0, uInt cacheSize=1)
Create a Standard storage manager with the given name.
casacore::StandardStMan::~StandardStMan
~StandardStMan()
casacore::StandardStMan::StandardStMan
StandardStMan(const StandardStMan &)=delete
Copy constructor cannot be used.
casacore::StandardStMan::StandardStMan
StandardStMan(const String &dataManagerName, Int bucketSize=0, uInt cacheSize=1)
casacore::StandardStMan::operator=
StandardStMan & operator=(const StandardStMan &)=delete
Assignment cannot be used.
casacore::String
String: the storage and methods of handling collections of characters.
Definition String.h:223
casacore
this file contains all the compiler specific defines
Definition mainpage.dox:28
casacore::uInt
unsigned int uInt
Definition aipstype.h:49
casacore::Int
int Int
Definition aipstype.h:48