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10.4.4. LFUAlgorithm - Least Frequently Used
org.jboss.cache.eviction.LFUAlgorithm controls the eviction in based on least frequently used algorithm. The least frequently used nodes will be the first to evict with this policy. Node usage starts at 1 when a node is first added. Each time it is visited, the node usage counter increments by 1. This number is used to determine which nodes are least frequently used. LFU is also a sorted eviction algorithm. The underlying EvictionQueue implementation and algorithm is sorted in ascending order of the node visits counter. This class guarantees a constant order ( O (1) ) for adds, removal and searches. However, when any number of nodes are added/visited to the queue for a given processing pass, a single quasilinear ( O (n * log n) ) operation is used to resort the queue in proper LFU order. Similarly if any nodes are removed or evicted, a single linear ( O (n) ) pruning operation is necessary to clean up the EvictionQueue. LFU has the following configuration parameters:
maxNodes- This is the maximum number of nodes allowed in this region. 0 denotes immediate expiry, -1 denotes no limit.minNodes- This is the minimum number of nodes allowed in this region. This value determines what the eviction queue should prune down to per pass. e.g. If minNodes is 10 and the cache grows to 100 nodes, the cache is pruned down to the 10 most frequently used nodes when the eviction timer makes a pass through the eviction algorithm.minTimeToLive- the minimum amount of time a node must be allowed to live after being accessed before it is allowed to be considered for eviction. 0 denotes that this feature is disabled, which is the default value.
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