org.jboss.cache.eviction
Class LFUAlgorithm

java.lang.Object
  org.jboss.cache.eviction.BaseEvictionAlgorithm
      org.jboss.cache.eviction.BaseSortedEvictionAlgorithm
          org.jboss.cache.eviction.LFUAlgorithm

All Implemented Interfaces:

EvictionAlgorithm

public class LFUAlgorithm
extends BaseSortedEvictionAlgorithm

Least Frequently Used algorithm for cache eviction. Note that this algorithm is not thread-safe.

This algorithm relies on maxNodes and minNodes to operate correctly. Eviction takes place using Least Frequently Used algorithm. A node A that is used less than a node B is evicted sooner.

The minNodes property defines a threshold for eviction. If minNodes = 100, the LFUAlgorithm will not evict the cache to anything less than 100 elements still left in cache. The maxNodes property defines the maximum number of nodes the cache will accept before eviction. maxNodes = 0 means that this region is unbounded. minNodes = 0 means that the eviction queue will attempt to bring the cache of this region to 0 elements (evict all elements) whenever it is run.

This algorithm uses a sorted eviction queue. The eviction queue is sorted in ascending order based on the number of times a node is visited. The more frequently a node is visited, the less likely it will be evicted.

Version:

$Revision: 7168 $

Author:

Daniel Huang - dhuang@jboss.org 10/2005

Field Summary

Fields inherited from class org.jboss.cache.eviction.BaseEvictionAlgorithm

allowTombstones, cache, configuration, evictionActionPolicy, evictionAlgorithmConfig, evictionQueue, recycleQueue, regionFqn

Constructor Summary

LFUAlgorithm()

Method Summary

java.lang.Class<? extends EvictionAlgorithmConfig>	getConfigurationClass() This is a helper so that the XML parser will be able to select and use the correct EvictionAlgorithmConfig implementation class corresponding to this EvictionAlgorithm.
protected void	prune()
protected EvictionQueue	setupEvictionQueue() Will create a LFUQueue to be used as the underlying eviction queue.
protected boolean	shouldEvictNode(NodeEntry ne) This method will check whether the given node should be evicted or not.

Methods inherited from class org.jboss.cache.eviction.BaseSortedEvictionAlgorithm

processQueues, resortEvictionQueue

Methods inherited from class org.jboss.cache.eviction.BaseEvictionAlgorithm

assignToRegion, canIgnoreEvent, emptyRecycleQueue, evict, evictCacheNode, getEvictionActionPolicy, getEvictionAlgorithmConfig, getEvictionQueue, getNextInQueue, initialize, isNodeInUseAndNotTimedOut, isYoungerThanMinimumTimeToLive, process, processAddedElement, processAddedNodes, processAddedNodes, processMarkInUseNodes, processRemovedElement, processRemovedNodes, processUnmarkInUseNodes, processVisitedNodes, resetEvictionQueue, setEvictionActionPolicy, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

LFUAlgorithm

public LFUAlgorithm()

Method Detail

shouldEvictNode

protected boolean shouldEvictNode(NodeEntry ne)

Description copied from class: BaseEvictionAlgorithm

This method will check whether the given node should be evicted or not.

Specified by:

shouldEvictNode in class BaseEvictionAlgorithm

Parameters:

ne - NodeEntry to test eviction for.

Returns:

True if the given node should be evicted. False if the given node should not be evicted.

setupEvictionQueue

protected EvictionQueue setupEvictionQueue()
                                    throws EvictionException

Will create a LFUQueue to be used as the underlying eviction queue.

Specified by:

setupEvictionQueue in class BaseEvictionAlgorithm

Returns:

The created LFUQueue.

Throws:

EvictionException

See Also:

EvictionQueue

prune

protected void prune()
              throws EvictionException

Overrides:

prune in class BaseEvictionAlgorithm

Throws:

EvictionException

getConfigurationClass

public java.lang.Class<? extends EvictionAlgorithmConfig> getConfigurationClass()

Description copied from interface: EvictionAlgorithm

This is a helper so that the XML parser will be able to select and use the correct EvictionAlgorithmConfig implementation class corresponding to this EvictionAlgorithm. E.g., the FIFOAlgorithm would return FIFOAlgorithmConfig.class.

Returns:

a class that is used to configure this EvictionAlgorithm.