org.apache.lucene.search

Class UsageTrackingQueryCachingPolicy

java.lang.Object

org.apache.lucene.search.UsageTrackingQueryCachingPolicy

All Implemented Interfaces:

QueryCachingPolicy

public final 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. It also uses some heuristics on segments, filters and the doc id sets that they produce in order to cache more aggressively when the execution cost significantly outweighs the caching overhead.

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

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.lucene.search.QueryCachingPolicy

QueryCachingPolicy.CacheOnLargeSegments

Field Summary

Fields inherited from interface org.apache.lucene.search.QueryCachingPolicy

ALWAYS_CACHE

Constructor Summary

Constructors

Constructor and Description
UsageTrackingQueryCachingPolicy() Create a new instance with an history size of 256.
UsageTrackingQueryCachingPolicy(int minIndexSize, float minSizeRatio, int historySize) Create a new instance.

Method Summary

Methods

Modifier and Type	Method and Description
protected int	minFrequencyToCache(Query query) For a given query, 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, LeafReaderContext context) Whether the given DocIdSet should be cached on a given segment.

Methods inherited from class java.lang.Object

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

Constructor Detail

UsageTrackingQueryCachingPolicy

public UsageTrackingQueryCachingPolicy(int minIndexSize,
                               float minSizeRatio,
                               int historySize)

Create a new instance.

Parameters:

minIndexSize - the minimum size of the top-level index

minSizeRatio - the minimum size ratio for segments to be cached, see QueryCachingPolicy.CacheOnLargeSegments

historySize - the number of recently used filters to track

UsageTrackingQueryCachingPolicy

public UsageTrackingQueryCachingPolicy()

Create a new instance with an history size of 256.

Method Detail

minFrequencyToCache

protected int minFrequencyToCache(Query query)

For a given query, return how many times it should appear in the history before being cached.

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,
                  LeafReaderContext context)
                    throws IOException

Description copied from interface: QueryCachingPolicy

Whether the given DocIdSet should be cached on a given segment. This method will be called on each leaf context to know if the filter should be cached on this particular leaf. The filter cache 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 set will be returned.

Specified by:

shouldCache in interface QueryCachingPolicy

Throws:

IOException