/*
* 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 final class BucketUtils {
private 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) {
if (finalSize < 1) {
throw new IllegalArgumentException("size must be positive, got " + finalSize);
}
if (numberOfShards < 1) {
throw new IllegalArgumentException("number of shards must be positive, got " + numberOfShards);
}
if (numberOfShards == 1) {
// In the case of a single shard, we do not need to over-request
return finalSize;
}
// Request 50% more buckets on the shards in order to improve accuracy
// as well as a small constant that should help with small values of 'size'
final long shardSampleSize = (long) (finalSize * 1.5 + 10);
return (int) Math.min(Integer.MAX_VALUE, shardSampleSize);
}
}