de.lmu.ifi.dbs.elki.persistent

Class LRUCache<P extends Page>

java.lang.Object

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

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

Type Parameters:

P - Page type

All Implemented Interfaces:

PageFile<P>, PageFileStatistics

public class LRUCache<P extends Page>
extends AbstractPageFile<P>

An LRU cache, based on LinkedHashMap.
This cache has a fixed maximum number of objects (cacheSize). If the cache is full and another object is added, the LRU (least recently used) object is dropped.

Field Summary

Fields

Modifier and Type	Field and Description
protected long	cacheSize The maximum number of objects in this cache.
protected long	cacheSizeBytes Cache size in bytes.
protected PageFile<P>	file The underlying file of this cache.
private static Logging	LOG Our logger
private LinkedHashMap<Integer,P>	map The map holding the objects of this cache.

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

readAccess, writeAccess

Constructor Summary

Constructors

Constructor and Description
LRUCache(long cacheSizeBytes, PageFile<P> file) Initializes this cache with the specified parameters.

Method Summary

Methods

Modifier and Type	Method and Description
void	clear() Clears this cache.
void	close() Closes this file.
void	deletePage(int pageID) Deletes the node with the specified id from this file.
protected void	expirePage(P page) Write page through to disk.
void	flush() Flushes this caches by writing any entry to the underlying file.
PageFileStatistics	getInnerStatistics() Get statistics for the inner page file, if present.
int	getNextPageID() Returns the next page id.
int	getPageSize() Get the page size of this page file.
boolean	initialize(PageHeader header) Initialize the page file with the given header - return "true" if the file already existed.
P	readPage(int pageID) Retrieves a page from the cache.
void	setCacheSize(int cacheSize) Sets the maximum size of this cache.
void	setNextPageID(int nextPageID) Sets the next page id.
int	setPageID(P page) Sets the id of the given page.
String	toString() Returns a string representation of this cache.
void	writePage(int pageID, P page) Perform the actual page write operation.

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, wait, wait, wait

Field Detail

LOG

private static final Logging LOG

Our logger

cacheSizeBytes

protected long cacheSizeBytes

Cache size in bytes.

cacheSize

protected long cacheSize

The maximum number of objects in this cache.

map

private LinkedHashMap<Integer,P extends Page> map

The map holding the objects of this cache.

file

protected PageFile<P extends Page> file

The underlying file of this cache. If an object is dropped it is written to the file.

Constructor Detail

LRUCache

public LRUCache(long cacheSizeBytes,
        PageFile<P> file)

Initializes this cache with the specified parameters.

Parameters:

cacheSizeBytes - the maximum number of pages in this cache

file - the underlying file of this cache, if a page is dropped it is written to the file

Method Detail

readPage

public P readPage(int pageID)

Retrieves a page from the cache. The retrieved page becomes the MRU (most recently used) page.

Parameters:

pageID - the id of the page to be returned

Returns:

the page associated to the id or null if no value with this key exists in the cache

writePage

public void writePage(int pageID,
             P page)

Description copied from class: AbstractPageFile

Perform the actual page write operation.

Specified by:

writePage in class AbstractPageFile<P extends Page>

Parameters:

pageID - Page id

page - Page to write

deletePage

public void deletePage(int pageID)

Description copied from interface: PageFile

Deletes the node with the specified id from this file.

Parameters:

pageID - the id of the node to be deleted

expirePage

protected void expirePage(P page)

Write page through to disk.

Parameters:

page - page

setPageID

public int setPageID(P page)

Description copied from interface: PageFile

Sets the id of the given page.

Parameters:

page - the page to set the id

Returns:

the page id

getNextPageID

public int getNextPageID()

Description copied from interface: PageFile

Returns the next page id.

Returns:

the next page id

setNextPageID

public void setNextPageID(int nextPageID)

Description copied from interface: PageFile

Sets the next page id.

Parameters:

nextPageID - the next page id to be set

getPageSize

public int getPageSize()

Description copied from interface: PageFile

Get the page size of this page file.

Returns:

page size

initialize

public boolean initialize(PageHeader header)

Description copied from interface: PageFile

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

Parameters:

header - Header

Returns:

true when the file already existed.

close

public void close()

Description copied from interface: PageFile

Closes this file.

Specified by:

close in interface PageFile<P extends Page>

Overrides:

close in class AbstractPageFile<P extends Page>

flush

public void flush()

Flushes this caches by writing any entry to the underlying file.

toString

public String toString()

Returns a string representation of this cache.

Overrides:

toString in class Object

Returns:

a string representation of this cache

clear

public void clear()

Clears this cache.

setCacheSize

public void setCacheSize(int cacheSize)

Sets the maximum size of this cache.

Parameters:

cacheSize - the cache size to be set

getInnerStatistics

public PageFileStatistics getInnerStatistics()

Description copied from interface: PageFileStatistics

Get statistics for the inner page file, if present.

Returns:

Inner page file statistics, or null.