http://lucene.apache.org/lucene-parent/lucene-core: Apache Lucene Java Core (The Apache Software Foundation) 
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 *     http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.lucene.search;


import java.io.IOException;


A policy defining which filters should be cached.
Implementations of this class must be thread-safe.

See Also:
@lucene.experimental
/**
 * A policy defining which filters should be cached.
 *
 * Implementations of this class must be thread-safe.
 *
 * @see UsageTrackingQueryCachingPolicy
 * @see LRUQueryCache
 * @lucene.experimental
 */
// TODO: add APIs for integration with IndexWriter.IndexReaderWarmer
public 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. 
/** 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. */
  void onUse(Query query);

  
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. 
/** Whether the given {@link Query} is worth caching.
   *  This method will be called by the {@link QueryCache} to know whether to
   *  cache. It will first attempt to load a {@link DocIdSet} from the cache.
   *  If it is not cached yet and this method returns <tt>true</tt> then a
   *  cache entry will be generated. Otherwise an uncached scorer will be
   *  returned. */
  boolean shouldCache(Query query) throws IOException;

}