Package 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 Details

    • 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 Details

    • 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