org.apache.lucene.search

Class UsageTrackingQueryCachingPolicy

java.lang.Object

org.apache.lucene.search.UsageTrackingQueryCachingPolicy

All Implemented Interfaces:

QueryCachingPolicy

public class UsageTrackingQueryCachingPolicy
extends Object
implements QueryCachingPolicy

A QueryCachingPolicy that tracks usage statistics of recently-used filters in order to decide on which filters are worth caching.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Constructor Summary

Constructors

Constructor and Description
UsageTrackingQueryCachingPolicy() Create a new instance with an history size of 256.
UsageTrackingQueryCachingPolicy(int historySize) Expert: Create a new instance with a configurable history size.

Method Summary

Modifier and Type	Method and Description
protected int	minFrequencyToCache(Query query) For a given filter, return how many times it should appear in the history before being cached.
void	onUse(Query query) Callback that is called every time that a cached filter is used.
boolean	shouldCache(Query query) Whether the given Query is worth caching.

Methods inherited from class java.lang.Object

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

Constructor Detail

UsageTrackingQueryCachingPolicy

public UsageTrackingQueryCachingPolicy(int historySize)

Expert: Create a new instance with a configurable history size. Beware of passing too large values for the size of the history, either minFrequencyToCache(org.apache.lucene.search.Query) returns low values and this means some filters that are rarely used will be cached, which would hurt performance. Or minFrequencyToCache(org.apache.lucene.search.Query) returns high values that are function of the size of the history but then filters will be slow to make it to the cache.

Parameters:

historySize - the number of recently used filters to track

UsageTrackingQueryCachingPolicy

public UsageTrackingQueryCachingPolicy()

Create a new instance with an history size of 256. This should be a good default for most cases.

Method Detail

minFrequencyToCache

protected int minFrequencyToCache(Query query)

For a given filter, return how many times it should appear in the history before being cached. The default implementation returns 2 for filters that need to evaluate against the entire index to build a DocIdSetIterator, like MultiTermQuery, point-based queries or TermInSetQuery, and 5 for other filters.

onUse

public void onUse(Query query)

Description copied from interface: QueryCachingPolicy

Callback that is called every time that a cached filter is used. This is typically useful if the policy wants to track usage statistics in order to make decisions.

Specified by:

onUse in interface QueryCachingPolicy

shouldCache

public boolean shouldCache(Query query)
                    throws IOException

Description copied from interface: QueryCachingPolicy

Whether the given Query is worth caching. This method will be called by the QueryCache to know whether to cache. It will first attempt to load a DocIdSet from the cache. If it is not cached yet and this method returns true then a cache entry will be generated. Otherwise an uncached scorer will be returned.

Specified by:

shouldCache in interface QueryCachingPolicy

Throws:

IOException