lucene/codecs/src/java/org/apache/lucene/codecs/bloom/BloomFilterFactory.java

/*
 * 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.lucene.codecs.bloom;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.SegmentWriteState;


/**
 * Class used to create index-time {@link FuzzySet} appropriately configured for
 * each field. Also called to right-size bitsets for serialization.
 * @lucene.experimental
 */
public abstract class BloomFilterFactory {
  
  /**
   * 
   * @param state  The content to be indexed
   * @param info
   *          the field requiring a BloomFilter
   * @return An appropriately sized set or null if no BloomFiltering required
   */
  public abstract FuzzySet getSetForField(SegmentWriteState state, FieldInfo info);
  
  /**
   * Called when downsizing bitsets for serialization
   * 
   * @param fieldInfo
   *          The field with sparse set bits
   * @param initialSet
   *          The bits accumulated
   * @return null or a hopefully more densely packed, smaller bitset
   */
  public FuzzySet downsize(FieldInfo fieldInfo, FuzzySet initialSet) {
    // Aim for a bitset size that would have 10% of bits set (so 90% of searches
    // would fail-fast)
    float targetMaxSaturation = 0.1f;
    return initialSet.downsize(targetMaxSaturation);
  }

  /**
   * Used to determine if the given filter has reached saturation and should be retired i.e. not saved any more
   * @param bloomFilter The bloomFilter being tested
   * @param fieldInfo The field with which this filter is associated
   * @return true if the set has reached saturation and should be retired
   */
  public abstract boolean isSaturated(FuzzySet bloomFilter, FieldInfo fieldInfo);
  
}