org.apache.lucene.search

Class 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.

    • Method Detail

      • 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