org.jboss.cache.eviction
Class LFUAlgorithm

java.lang.Object
  extended by org.jboss.cache.eviction.BaseEvictionAlgorithm
      extended by org.jboss.cache.eviction.BaseSortedEvictionAlgorithm
          extended by org.jboss.cache.eviction.LFUAlgorithm
All Implemented Interfaces:
EvictionAlgorithm

public class LFUAlgorithm
extends BaseSortedEvictionAlgorithm
implements EvictionAlgorithm

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: 1.4 $
Author:
Daniel Huang - dhuang@jboss.org 10/2005

Field Summary
 
Fields inherited from class org.jboss.cache.eviction.BaseEvictionAlgorithm
evictionQueue, recycleQueue, region
 
Constructor Summary
LFUAlgorithm()
           
 
Method Summary
protected  void prune()
           
protected  EvictionQueue setupEvictionQueue(Region region)
          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
process, processQueues, resortEvictionQueue
 
Methods inherited from class org.jboss.cache.eviction.BaseEvictionAlgorithm
emptyRecycleQueue, evict, evictCacheNode, getEvictionQueue, initialize, isNodeInUseAndNotTimedOut, processAddedElement, processAddedNodes, processMarkInUseNodes, processRemovedElement, processRemovedNodes, processUnmarkInUseNodes, processVisitedNodes, resetEvictionQueue
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface org.jboss.cache.eviction.EvictionAlgorithm
getEvictionQueue, process, resetEvictionQueue
 

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(Region region)
                                    throws EvictionException
Will create a LFUQueue to be used as the underlying eviction queue.

Specified by:
setupEvictionQueue in class BaseEvictionAlgorithm
Parameters:
region - Region to create the eviction queue for.
Returns:
The created LFUQueue.
Throws:
EvictionException
See Also:
EvictionQueue

prune

protected void prune()
              throws EvictionException
Overrides:
prune in class BaseEvictionAlgorithm
Throws:
EvictionException


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