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* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.search.aggregations.bucket;
/**
* Helper functions for common Bucketing functions
*/
public class BucketUtils {
/**
* Heuristic used to determine the size of shard-side PriorityQueues when
* selecting the top N terms from a distributed index.
*
* @param finalSize
* The number of terms required in the final reduce phase.
* @param numberOfShards
* The number of shards being queried.
* @return A suggested default for the size of any shard-side PriorityQueues
*/
public static int suggestShardSideQueueSize(int finalSize, int numberOfShards) {
assert numberOfShards >= 1;
if (numberOfShards == 1) {
return finalSize;
}
//Cap the multiplier used for shards to avoid excessive data transfer
final long shardSampleSize = (long) finalSize * Math.min(10, numberOfShards);
// When finalSize is very small e.g. 1 and there is a low number of
// shards then we need to ensure we still gather a reasonable sample of statistics from each
// shard (at low cost) to improve the chances of the final result being accurate.
return (int) Math.min(Integer.MAX_VALUE, Math.max(10, shardSampleSize));
}
}