org.apache.lucene.search

Class CachingCollector

java.lang.Object

org.apache.lucene.search.FilterCollector

org.apache.lucene.search.CachingCollector

All Implemented Interfaces:

Collector

public abstract class CachingCollector
extends FilterCollector

Caches all docs, and optionally also scores, coming from a search, and is then able to replay them to another collector. You specify the max RAM this class may use. Once the collection is done, call isCached(). If this returns true, you can use replay(Collector) against a new collector. If it returns false, this means too much RAM was required and you must instead re-run the original search.

NOTE: this class consumes 4 (or 8 bytes, if scoring is cached) per collected document. If the result set is large this can easily be a very substantial amount of RAM!

See the Lucene modules/grouping module for more details including a full code example.

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

Field Summary

Fields inherited from class org.apache.lucene.search.FilterCollector

in

Method Summary

Modifier and Type	Method and Description
static CachingCollector	create(boolean cacheScores, double maxRAMMB) Creates a CachingCollector which does not wrap another collector.
static CachingCollector	create(Collector other, boolean cacheScores, double maxRAMMB) Create a new CachingCollector that wraps the given collector and caches documents and scores up to the specified RAM threshold.
static CachingCollector	create(Collector other, boolean cacheScores, int maxDocsToCache) Create a new CachingCollector that wraps the given collector and caches documents and scores up to the specified max docs threshold.
boolean	isCached() Return true is this collector is able to replay collection.
abstract void	replay(Collector other) Replays the cached doc IDs (and scores) to the given Collector.

Methods inherited from class org.apache.lucene.search.FilterCollector

getLeafCollector, scoreMode, toString

Methods inherited from class java.lang.Object

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

Method Detail

create

public static CachingCollector create(boolean cacheScores,
                                      double maxRAMMB)

Creates a CachingCollector which does not wrap another collector. The cached documents and scores can later be replayed.

create

public static CachingCollector create(Collector other,
                                      boolean cacheScores,
                                      double maxRAMMB)

Create a new CachingCollector that wraps the given collector and caches documents and scores up to the specified RAM threshold.

Parameters:

other - the Collector to wrap and delegate calls to.

cacheScores - whether to cache scores in addition to document IDs. Note that this increases the RAM consumed per doc

maxRAMMB - the maximum RAM in MB to consume for caching the documents and scores. If the collector exceeds the threshold, no documents and scores are cached.

create

public static CachingCollector create(Collector other,
                                      boolean cacheScores,
                                      int maxDocsToCache)

Create a new CachingCollector that wraps the given collector and caches documents and scores up to the specified max docs threshold.

Parameters:

other - the Collector to wrap and delegate calls to.

cacheScores - whether to cache scores in addition to document IDs. Note that this increases the RAM consumed per doc

maxDocsToCache - the maximum number of documents for caching the documents and possible the scores. If the collector exceeds the threshold, no documents and scores are cached.

isCached

public final boolean isCached()

Return true is this collector is able to replay collection.

replay

public abstract void replay(Collector other)
                     throws IOException

Replays the cached doc IDs (and scores) to the given Collector. If this instance does not cache scores, then Scorer is not set on other.setScorer as well as scores are not replayed.

Throws:

IllegalStateException - if this collector is not cached (i.e., if the RAM limits were too low for the number of documents + scores to cache).

IllegalArgumentException - if the given Collect's does not support out-of-order collection, while the collector passed to the ctor does.

IOException