de.lmu.ifi.dbs.elki.persistent

Class PersistentPageFile<P extends ExternalizablePage>

java.lang.Object

de.lmu.ifi.dbs.elki.persistent.AbstractPageFile<P>

de.lmu.ifi.dbs.elki.persistent.AbstractStoringPageFile<P>

de.lmu.ifi.dbs.elki.persistent.PersistentPageFile<P>

Type Parameters:

P - Page type

All Implemented Interfaces:

PageFile<P>, PageFileStatistics

public class PersistentPageFile<P extends ExternalizablePage>
extends AbstractStoringPageFile<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.

Field Summary

Fields

Modifier and Type	Field and Description
private static int	EMPTY_PAGE Indicates an empty page.
private boolean	existed Whether we are initializing from an existing file.
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.
private static Logging	LOG Our logger
protected Class<P>	pageclass The type of pages we use.

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

emptyPages, nextPageID, pageSize

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

readAccess, writeAccess

Constructor Summary

Constructors

Constructor and Description
PersistentPageFile(int pageSize, String fileName, Class<P> pageclass) Creates a new PersistentPageFile from an existing file.

Method Summary

Methods

Modifier and Type	Method and Description
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.
boolean	initialize(PageHeader header) Initialize the page file with the given header - return "true" if the file already existed.
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.
void	writePage(int pageID, 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.

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

getInnerStatistics, getNextPageID, getPageSize, setPageID

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

getReadOperations, getWriteOperations, resetPageAccess, writePage

Methods inherited from class java.lang.Object

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

Field Detail

LOG

private static final Logging LOG

Our logger

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 PageHeader header

The header of this page file.

pageclass

protected final Class<P extends ExternalizablePage> pageclass

The type of pages we use.

existed

private boolean existed

Whether we are initializing from an existing file.

Constructor Detail

PersistentPageFile

public PersistentPageFile(int pageSize,
                  String fileName,
                  Class<P> pageclass)

Creates a new PersistentPageFile from an existing file.

Parameters:

pageSize - the page size

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.

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.

Specified by:

deletePage in interface PageFile<P extends ExternalizablePage>

Overrides:

deletePage in class AbstractStoringPageFile<P extends ExternalizablePage>

Parameters:

pageID - the id of the node to be deleted

writePage

public void writePage(int pageID,
             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.

Specified by:

writePage in class AbstractPageFile<P extends ExternalizablePage>

Parameters:

page - the page which has to be written to disk

pageID - Page id

close

public void close()

Closes this file.

Specified by:

close in interface PageFile<P extends ExternalizablePage>

Overrides:

close in class AbstractPageFile<P extends ExternalizablePage>

clear

public void clear()

Clears this PageFile.

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.

Specified by:

setNextPageID in interface PageFile<P extends ExternalizablePage>

Overrides:

setNextPageID in class AbstractStoringPageFile<P extends ExternalizablePage>

Parameters:

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

initialize

public boolean initialize(PageHeader header)

Description copied from class: AbstractStoringPageFile

Initialize the page file with the given header - return "true" if the file already existed.

Specified by:

initialize in interface PageFile<P extends ExternalizablePage>

Overrides:

initialize in class AbstractStoringPageFile<P extends ExternalizablePage>

Parameters:

header - Header

Returns:

true when the file already existed.