content: /**
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.apache.solr.search;
  
  /* Copyright (c) 2003 The Nutch Organization.  All rights reserved.   */
  /* Use subject to the conditions in http://www.nutch.org/LICENSE.txt. */
  
  
  import org.apache.lucene.search.*;
  
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.io.IOException;
  
  /** Utility which converts certain query clauses into {@link QueryFilter}s and
   * caches these.  Only required {@link TermQuery}s whose boost is zero and
   * whose term occurs in at least a certain fraction of documents are converted
   * to cached filters.  This accelerates query constraints like language,
   * document format, etc., which do not affect ranking but might otherwise slow
   * search considerably. */
  // Taken from Nutch and modified - YCS
  class LuceneQueryOptimizer {
    private LinkedHashMap cache;                   // an LRU cache of QueryFilter
  
    private float threshold;
  
    /** Construct an optimizer that caches and uses filters for required {@link
     * TermQuery}s whose boost is zero.
     * @param cacheSize the number of QueryFilters to cache
     * @param threshold the fraction of documents which must contain term
     */
    public LuceneQueryOptimizer(final int cacheSize, float threshold) {
      this.cache = new LinkedHashMap(cacheSize, 0.75f, true) {
          @Override
          protected boolean removeEldestEntry(Map.Entry eldest) {
            return size() > cacheSize;              // limit size of cache
          }
        };
      this.threshold = threshold;
    }
  
    public TopDocs optimize(BooleanQuery original,
                            Searcher searcher,
                            int numHits,
                            Query[] queryOut,
                            Filter[] filterOut
                            )
      throws IOException {
  
      BooleanQuery query = new BooleanQuery();
      BooleanQuery filterQuery = null;
  
      for (BooleanClause c : original.clauses()) {
  
  /***
  System.out.println("required="+c.required);
  System.out.println("boost="+c.query.getBoost());
  System.out.println("isTermQuery="+(c.query instanceof TermQuery));
  if (c.query instanceof TermQuery) {
   System.out.println("term="+((TermQuery)c.query).getTerm());
   System.out.println("docFreq="+searcher.docFreq(((TermQuery)c.query).getTerm()));
  }
  ***/
        Query q = c.getQuery();
        if (c.isRequired()                              // required
            && q.getBoost() == 0.0f           // boost is zero
            && q instanceof TermQuery         // TermQuery
            && (searcher.docFreq(((TermQuery)q).getTerm())
                / (float)searcher.maxDoc()) >= threshold) { // check threshold
          if (filterQuery == null)
            filterQuery = new BooleanQuery();
          filterQuery.add(q, BooleanClause.Occur.MUST);    // filter it
  //System.out.println("WooHoo... qualified to be hoisted to a filter!");
        } else {
          query.add(c);                             // query it
        }
      }
  
      Filter filter = null;
      if (filterQuery != null) {
        synchronized (cache) {                      // check cache
          filter = (Filter)cache.get(filterQuery);
        }
        if (filter == null) {                       // miss
          filter = new CachingWrapperFilter(new QueryWrapperFilter(filterQuery)); // construct new entry
          synchronized (cache) {
            cache.put(filterQuery, filter);         // cache it
          }
        }        
      }
  
      // YCS: added code to pass out optimized query and filter
      // so they can be used with Hits
      if (queryOut != null && filterOut != null) {
        queryOut[0] = query; filterOut[0] = filter;
        return null;
      } else {
        return searcher.search(query, filter, numHits);
      }
  
    }
  }
  