Package org.apache.lucene.search

Class CachingCollector

java.lang.Object

org.apache.lucene.search.Collector

org.apache.lucene.search.CachingCollector

public abstract class CachingCollector
extends Collector

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!

NOTE: this class caches at least 128 documents before checking RAM limits.

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

Method Summary

Modifier and Type	Method	Description
boolean	acceptsDocsOutOfOrder()	Return true if this collector does not require the matching docIDs to be delivered in int sort order (smallest to largest) to Collector.collect(int).
static CachingCollector	create(boolean acceptDocsOutOfOrder, 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()
abstract void	replay(Collector other)	Replays the cached doc IDs (and scores) to the given Collector.
void	setNextReader(AtomicReaderContext context)	Called before collecting from each AtomicReaderContext.

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

collect, setScorer

Methods inherited from class java.lang.Object

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

Method Detail

create

public static CachingCollector create(boolean acceptDocsOutOfOrder,
                                      boolean cacheScores,
                                      double maxRAMMB)

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

Parameters:

acceptDocsOutOfOrder - whether documents are allowed to be collected out-of-order

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.

acceptsDocsOutOfOrder

public boolean acceptsDocsOutOfOrder()

Description copied from class: Collector

Return true if this collector does not require the matching docIDs to be delivered in int sort order (smallest to largest) to Collector.collect(int).

Most Lucene Query implementations will visit matching docIDs in order. However, some queries (currently limited to certain cases of BooleanQuery) can achieve faster searching if the Collector allows them to deliver the docIDs out of order.

Many collectors don't mind getting docIDs out of order, so it's important to return true here.

Specified by:

acceptsDocsOutOfOrder in class Collector

isCached

public boolean isCached()

setNextReader

public void setNextReader(AtomicReaderContext context)
                   throws java.io.IOException

Description copied from class: Collector

Called before collecting from each AtomicReaderContext. All doc ids in Collector.collect(int) will correspond to IndexReaderContext.reader(). Add AtomicReaderContext.docBase to the current IndexReaderContext.reader()'s internal document id to re-base ids in Collector.collect(int).

Specified by:

setNextReader in class Collector

Parameters:

context - next atomic reader context

Throws:

java.io.IOException

replay

public abstract void replay(Collector other)
                     throws java.io.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:

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

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

java.io.IOException