Package org.cache2k.core.eviction

Class ClockProPlusEviction

java.lang.Object

org.cache2k.core.eviction.AbstractEviction

org.cache2k.core.eviction.ClockProPlusEviction

All Implemented Interfaces:

NeedsClose, Eviction

public class ClockProPlusEviction
extends AbstractEviction

Eviction algorithm inspired from CLOCK Pro with 3 clocks.

Uses a static allocation for hot and cold space sizes. No online or dynamic optimization is done yet. However, the hit rate for all measured access traces is better than LRU and resistant to scans.

From cache2k version 1.2 to version 1.4 the implementation was simplified and the demotion of hot entries removed. The result achieves similar or better hit rates. Version 2.4 limits the ghost size to 3000 elements. Version 2.6 stops inserting evicted hot entries into ghosts.

The Clock-Pro algorithm is explained by the authors in CLOCK-Pro: An Effective Improvement of the CLOCK Replacement and Clock-Pro: An Effective Replacement in OS Kernel.

Author:

Jens Wilke

Field Summary

Fields inherited from class org.cache2k.core.eviction.AbstractEviction

heapCache, idleNonEvictDrainCount, idleScanRound, lock, MAXIMAL_CHUNK_SIZE, maxSize, maxWeight, MINIMAL_CHUNK_SIZE, MINIMUM_CAPACITY_FOR_CHUNKING

Constructor Summary

Constructors

Constructor	Description
ClockProPlusEviction(HeapCacheForEviction heapCache, InternalEvictionListener listener, long maxSize, org.cache2k.operation.Weigher weigher, long maxWeight, boolean noChunking)

Method Summary

Modifier and Type	Method	Description
void	checkIntegrity(IntegrityState integrityState)
protected Entry	findEvictionCandidate()	Runs cold hand and in turn hot hand to find eviction candidate.
protected Entry	findIdleCandidate(int maxScan)	Find idle candidate.
protected Entry	findIdleInHot(int maxScan)
long	getGhostMax()
long	getHotMax()
protected long	getScanCount()
long	getSize()
protected void	insertIntoReplacementList(Entry e)	Place the entry as a new entry into the eviction data structures.
protected long	removeAllFromReplacementList()	Remove entries from the replacement list without locking the entry itself.
protected void	removeFromReplacementList(Entry e)	Remove, expire or eviction of an entry happens.
void	removeFromReplacementListOnEvict(Entry e)	Track the entry on the ghost list and call the usual remove procedure.
String	toString()
protected void	updateHotMax()	Updates hot max based on current size.

Methods inherited from class org.cache2k.core.eviction.AbstractEviction

changeCapacity, close, evictEventually, evictEventuallyBeforeInsert, evictEventuallyBeforeInsertOnSegment, evictIdleEntries, getMetrics, isWeigherPresent, removeAll, runLocked, startNewIdleScanRound, submitWithoutTriggeringEviction, updateAccumulatedWeightInLock, updateTotalWeightForRemove, updateWeight

Methods inherited from class java.lang.Object

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

Constructor Detail

ClockProPlusEviction

public ClockProPlusEviction(HeapCacheForEviction heapCache,
                            InternalEvictionListener listener,
                            long maxSize,
                            org.cache2k.operation.Weigher weigher,
                            long maxWeight,
                            boolean noChunking)

Method Detail

getHotMax

public long getHotMax()

getGhostMax

public long getGhostMax()

updateHotMax

protected void updateHotMax()

Updates hot max based on current size. This is called when eviction kicks in so current size is the maximum size this cache should reach regardless whether we use entry capacity or weigher to limit the size.

Specified by:

updateHotMax in class AbstractEviction

removeAllFromReplacementList

protected long removeAllFromReplacementList()

Description copied from class: AbstractEviction

Remove entries from the replacement list without locking the entry itself.

Specified by:

removeAllFromReplacementList in class AbstractEviction

removeFromReplacementListOnEvict

public void removeFromReplacementListOnEvict(Entry e)

Track the entry on the ghost list and call the usual remove procedure.

Specified by:

removeFromReplacementListOnEvict in class AbstractEviction

removeFromReplacementList

protected void removeFromReplacementList(Entry e)

Remove, expire or eviction of an entry happens. Remove the entry from the replacement list data structure.

Why don't generate ghosts here? If the entry is removed because of a programmatic remove or expiry we should not occupy any resources. Removing and expiry may also take place when no eviction is needed at all, which happens when the cache size did not hit the maximum yet. Producing ghosts would add additional overhead, when it is not needed.

Specified by:

removeFromReplacementList in class AbstractEviction

getSize

public long getSize()

Specified by:

getSize in class AbstractEviction

insertIntoReplacementList

protected void insertIntoReplacementList(Entry e)

Description copied from class: AbstractEviction

Place the entry as a new entry into the eviction data structures.

Specified by:

insertIntoReplacementList in class AbstractEviction

findIdleCandidate

protected Entry findIdleCandidate(int maxScan)

Find idle candidate. Idle scanning does scan on the bigger clock first, which is typically the hot clock, because entries are sitting in the cache for the longest time.

Specified by:

findIdleCandidate in class AbstractEviction

findIdleInHot

protected Entry findIdleInHot(int maxScan)

findEvictionCandidate

protected Entry findEvictionCandidate()

Runs cold hand and in turn hot hand to find eviction candidate.

Specified by:

findEvictionCandidate in class AbstractEviction

getScanCount

protected long getScanCount()

Specified by:

getScanCount in class AbstractEviction

checkIntegrity

public void checkIntegrity(IntegrityState integrityState)

toString

public String toString()

Overrides:

toString in class AbstractEviction