com.trivago.triava.tcache.eviction

Class LFUEviction<K,V>

java.lang.Object

com.trivago.triava.tcache.eviction.FreezingEvictor<K,V>

com.trivago.triava.tcache.eviction.LFUEviction<K,V>

Type Parameters:

K - Key class

V - Value class

All Implemented Interfaces:

EvictionInterface<K,V>, Serializable

public class LFUEviction<K,V>
extends FreezingEvictor<K,V>

LFU eviction based on use count

Author:

cesken

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
LFUEviction()

Method Summary

Modifier and Type	Method and Description
long	getFreezeValue(K key, TCacheHolder<V> holder) Returns a value for the given key, that may be used by the concrete implementation of the #evictionComparator().

Methods inherited from class com.trivago.triava.tcache.eviction.FreezingEvictor

afterEviction, beforeEviction, compareByFreezer, evictionComparator

Methods inherited from class java.lang.Object

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

Constructor Detail

LFUEviction

public LFUEviction()

Method Detail

getFreezeValue

public long getFreezeValue(K key,
                           TCacheHolder<V> holder)

Description copied from class: FreezingEvictor

Returns a value for the given key, that may be used by the concrete implementation of the #evictionComparator(). The default comparator returned by FreezingEvictor#evictionComparator() chooses keys with smaller values to be evicted sooner than those with bigger values (comparable to Comparator.compare(Object, Object)). While it is recommended to conform to this, it is not required - own implementations may use any other strategy, but should document this clearly.

There are three typical usage patterns:

• MUST implement: There is a relevant mutable value, for example metadata like use count or the last use timestamp. In this case you MUST implement this method.
• SHOULD implement: The relevant value is expensive to calculate. In this case you SHOULD implement this method for performance reasons, as the value is likely required many times during sorting.
• NOT USED: For other cases, this method should return 0.

If the implementing class does not require such a value, it should return 0. Typical examples are element metadata like use count or the last use timestamp. Content-aware eviction implementations can also derive a value from the data, like session status ("logged out", "idle").

Specified by:

getFreezeValue in interface EvictionInterface<K,V>

Specified by:

getFreezeValue in class FreezingEvictor<K,V>

Parameters:

key - The key

holder - The holder that holds the associated value for the key

Returns:

Use count