casacore::MultiFile Class Reference

Class to combine multiple files in a single one. More...

#include <MultiFile.h>

Inheritance diagram for casacore::MultiFile:

Public Member Functions
	MultiFile (const String &name, ByteIO::OpenOption, Int blockSize=0)
	Open or create a MultiFile with the given name.
virtual	~MultiFile ()
	The destructor flushes and closes the file.
virtual void	reopenRW ()
	Reopen the underlying file for read/write access.
virtual void	fsync ()
	Fsync the file (i.e., force the data to be physically written).
Private Member Functions
virtual void	doAddFile (MultiFileInfo &)
	Do the class-specific actions on adding a file.
virtual void	doDeleteFile (MultiFileInfo &)
	Do the class-specific actions on deleting a file.
virtual void	flushFile ()
	Flush the file itself.
virtual void	close ()
	Flush and close the file.
virtual void	writeHeader ()
	Write the header info.
virtual void	readHeader (Bool always=True)
	Read the header info.
virtual void	extend (MultiFileInfo &info, Int64 lastblk)
	Extend the virtual file to fit lastblk.
virtual void	writeBlock (MultiFileInfo &info, Int64 blknr, const void *buffer)
	Write a data block.
virtual void	readBlock (MultiFileInfo &info, Int64 blknr, void *buffer)
	Read a data block.
Private Attributes
FiledesIO	itsIO
int	itsFD

Detailed Description

Class to combine multiple files in a single one.

Intended use:

Public interface

Review Status

Test programs:: tMultiFile

Synopsis

This class is a container file holding multiple virtual files. It is primarily meant as a container file for the storage manager files of a table to reduce the number of files used (especially for Lustre) and to reduce the number of open files (especially when concatenating tables).
A secondary goal is offering the ability to use an IO buffer size that matches the file system well (large buffer size for e.g. ZFS).

The SetupNewTable constructor has a StorageOption argument to define if a MultiFile has to be used and if so, the buffer size to use. It is also possible to specify that through aipsrc variables.

A virtual file is spread over multiple (fixed size) data blocks in the MultiFile. A data block is never shared by multiple files. For each virtual file MultiFile keeps a MultiFileInfo object telling the file size and the blocks numbers used for the file. When flushing the MultiFile, this meta info is written into the header block. If it does not fit in the header block, the rest is written in a separate "-ext" file. if needed, continuation blocks. On open and resync, it is read back.

A virtual file is represented by an MFFileIO object, which is derived from ByteIO and as such part of the casacore IO framework. It makes it possible for applications to access a virtual file in the same way as a regular file.

It is possible to delete a virtual file. Its blocks will be added to the free block list (which is also stored in the meta info).

Example

In principle it is possible to use the MultiFile functions directly. However, in general it is much easier to use an MFFileIO object per virtual file as shown below.

 // Create a new MultiFile using a block size of 1 MB.
 MultiFile mfile("file.mf', ByteIO::New, 1048576);
 // Create a virtual file in it.
 MFFileIO mf1(mfile, "mf1", ByteIO::New);
 // Use it (for example) as the sink of AipsIO.
 AipsIO stream (&mf1);
 // Write values.
 stream << (Int)10;
 stream << True;
 // Seek to beginning of file and read data in.
 stream.setpos (0);
 Int vali;
 Bool valb;
 stream >> vali >> valb;

To Do

write headers at alternating file positions (for robustness)
possibly write headers entirely at the end if larger than blocksize

Definition at line 108 of file MultiFile.h.

Constructor & Destructor Documentation

casacore::MultiFile::MultiFile	(	const String &	name,
		ByteIO::OpenOption	,
		Int	blockSize = `0`
	)

Open or create a MultiFile with the given name.

Upon creation the block size can be given. If 0, it uses the block size of the file system the file is on.

virtual casacore::MultiFile::~MultiFile ( ) [virtual]

The destructor flushes and closes the file.

Member Function Documentation

virtual void casacore::MultiFile::close ( ) [private, virtual]

Flush and close the file.

Implements casacore::MultiFileBase.

virtual void casacore::MultiFile::doAddFile ( MultiFileInfo & ) [private, virtual]

Do the class-specific actions on adding a file.

Implements casacore::MultiFileBase.

virtual void casacore::MultiFile::doDeleteFile ( MultiFileInfo & ) [private, virtual]

Do the class-specific actions on deleting a file.

Implements casacore::MultiFileBase.

virtual void casacore::MultiFile::extend	(	MultiFileInfo &	info,
		Int64	lastblk
	)			`[private, virtual]`

Extend the virtual file to fit lastblk.

Implements casacore::MultiFileBase.

virtual void casacore::MultiFile::flushFile ( ) [private, virtual]

Flush the file itself.

Implements casacore::MultiFileBase.

virtual void casacore::MultiFile::fsync ( ) [virtual]

Fsync the file (i.e., force the data to be physically written).

Implements casacore::MultiFileBase.

virtual void casacore::MultiFile::readBlock	(	MultiFileInfo &	info,
		Int64	blknr,
		void *	buffer
	)			`[private, virtual]`

Read a data block.

Implements casacore::MultiFileBase.

virtual void casacore::MultiFile::readHeader ( Bool always = True ) [private, virtual]

Read the header info.

If always==False, the info is only read if the header counter has changed.

Implements casacore::MultiFileBase.

virtual void casacore::MultiFile::reopenRW ( ) [virtual]

Reopen the underlying file for read/write access.

Nothing will be done if the file is writable already. Otherwise it will be reopened and an exception will be thrown if it is not possible to reopen it for read/write access.

Implements casacore::MultiFileBase.