de.lmu.ifi.dbs.elki.persistent
Class PersistentPageFile<P extends Page<P>>

java.lang.Object
  de.lmu.ifi.dbs.elki.persistent.PageFile<P>
      de.lmu.ifi.dbs.elki.persistent.PersistentPageFile<P>

Type Parameters:

P - Page type

All Implemented Interfaces:

CachedFile<P>

public class PersistentPageFile<P extends Page<P>>
extends PageFile<P>

A PersistentPageFile stores objects persistently that implement the Page interface. For convenience each page is represented by a single file. All pages are stored in a specified directory.

Author:

Elke Achtert

Field Summary

private static int	EMPTY_PAGE Indicates an empty page.
private RandomAccessFile	file The file storing the pages.
private static int	FILLED_PAGE Indicates a filled page.
protected PageHeader	header The header of this page file.
protected Class<? extends P>	pageclass The type of pages we use.

Fields inherited from class de.lmu.ifi.dbs.elki.persistent.PageFile

cache, emptyPages, nextPageID, pageSize, readAccess, writeAccess

Constructor Summary

PersistentPageFile(PageHeader header, long cacheSize, Cache<P> cache, String fileName, Class<? extends P> pageclass)
Creates a new PersistentPageFile from an existing file.

Method Summary

private P	byteArrayToPage(byte[] array) Reconstruct a serialized object from the specified byte array.
void	clear() Clears this PageFile.
void	close() Closes this file.
void	deletePage(int pageID) Deletes the node with the specified id from this file.
RandomAccessFile	getFile()
PageHeader	getHeader() Get the header of this persistent page file.
void	increaseReadAccess() Increases the readAccess counter by one.
void	increaseWriteAccess() Increases the writeAccess counter by one.
void	objectRemoved(P page) This method is called by the cache if the page is not longer stored in the cache and has to be written to disk.
private byte[]	pageToByteArray(P page) Serializes an object into a byte array.
P	readPage(int pageID) Reads the page with the given id from this file.
void	setNextPageID(int next_page_id) Set the next page id to the given value.

Methods inherited from class de.lmu.ifi.dbs.elki.persistent.PageFile

getLogicalPageAccess, getNextPageID, getPhysicalReadAccess, getPhysicalWriteAccess, initCache, resetPageAccess, setCacheSize, setPageID, writePage

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

EMPTY_PAGE

private static final int EMPTY_PAGE

Indicates an empty page.

See Also:

Constant Field Values

FILLED_PAGE

private static final int FILLED_PAGE

Indicates a filled page.

See Also:

Constant Field Values

file

private final RandomAccessFile file

The file storing the pages.

header

protected final PageHeader header

The header of this page file.

pageclass

protected final Class<? extends P extends Page<P>> pageclass

The type of pages we use.

Constructor Detail

PersistentPageFile

public PersistentPageFile(PageHeader header,
                          long cacheSize,
                          Cache<P> cache,
                          String fileName,
                          Class<? extends P> pageclass)

Creates a new PersistentPageFile from an existing file.

Parameters:

header - the header of this file

fileName - the name of the file

cacheSize - the size of the cache in Byte

cache - the class of the cache to be used

pageclass - the class of pages to be used

Method Detail

readPage

public P readPage(int pageID)

Reads the page with the given id from this file.

Overrides:

readPage in class PageFile<P extends Page<P>>

Parameters:

pageID - the id of the page to be returned

Returns:

the page with the given pageId

deletePage

public void deletePage(int pageID)

Deletes the node with the specified id from this file.

Overrides:

deletePage in class PageFile<P extends Page<P>>

Parameters:

pageID - the id of the node to be deleted

objectRemoved

public void objectRemoved(P page)

This method is called by the cache if the page is not longer stored in the cache and has to be written to disk.

Parameters:

page - the page which has to be written to disk

close

public void close()

Closes this file.

Overrides:

close in class PageFile<P extends Page<P>>

clear

public void clear()

Clears this PageFile.

Overrides:

clear in class PageFile<P extends Page<P>>

byteArrayToPage

private P byteArrayToPage(byte[] array)

Reconstruct a serialized object from the specified byte array.

Parameters:

array - the byte array from which the object should be reconstructed

Returns:

a serialized object from the specified byte array

pageToByteArray

private byte[] pageToByteArray(P page)

Serializes an object into a byte array.

Parameters:

page - the object to be serialized

Returns:

the byte array

getFile

public RandomAccessFile getFile()

Returns:

the random access file storing the pages.

getHeader

public PageHeader getHeader()

Get the header of this persistent page file.

Returns:

the header used by this page file

increaseReadAccess

public void increaseReadAccess()

Increases the readAccess counter by one.

increaseWriteAccess

public void increaseWriteAccess()

Increases the writeAccess counter by one.

setNextPageID

public void setNextPageID(int next_page_id)

Set the next page id to the given value. If this means that any page ids stored in emptyPages are smaller than next_page_id, they are removed from this file's observation stack.

Overrides:

setNextPageID in class PageFile<P extends Page<P>>

Parameters:

next_page_id - the id of the next page to be inserted (if there are no more empty pages to be filled)