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Apache Solr (module: core)

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/*
 * 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.handler.component;

import java.io.IOException;
import java.util.Comparator;
import org.apache.solr.search.SolrIndexSearcher;

/**
 * The MergeStrategy class defines custom merge logic for distributed searches.
 *
 * Note: This API is experimental and may change in non backward-compatible ways in the
 * future
 */
public interface MergeStrategy {

  /**
   * merge defines the merging behaving of results that are collected from the shards during a
   * distributed search.
   */
  public void merge(ResponseBuilder rb, ShardRequest sreq);

  /**
   * mergesIds must return true if the merge method merges document ids from the shards. If it
   * merges other output from the shards it must return false.
   */
  public boolean mergesIds();

  /**
   * handlesMergeFields must return true if the MergeStrategy implements a custom
   * handleMergeFields(ResponseBuilder rb, SolrIndexSearch searcher)
   */
  public boolean handlesMergeFields();

  /**
   * Implement handleMergeFields(ResponseBuilder rb, SolrIndexSearch searcher) if your merge
   * strategy needs more complex data then the sort fields provide.
   */
  public void handleMergeFields(ResponseBuilder rb, SolrIndexSearcher searcher) throws IOException;

  /** Defines the order that the mergeStrategies are applied. Lower costs are applied first. */
  public int getCost();

  Comparator MERGE_COMP = Comparator.comparingInt(MergeStrategy::getCost);
}