org.apache.druid.server.router.RendezvousHasher.java Source code

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Here is the source code for org.apache.druid.server.router.RendezvousHasher.java

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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.druid.server.router;

import com.google.common.collect.Lists;
import com.google.common.hash.HashCode;
import com.google.common.hash.HashFunction;
import com.google.common.hash.Hashing;

import java.nio.charset.StandardCharsets;
import java.util.List;
import java.util.Set;

/**
 * Distributes objects across a set of node keys using rendezvous hashing
 * See https://en.wikipedia.org/wiki/Rendezvous_hashing
 */
public class RendezvousHasher {
    private static final HashFunction HASH_FN = Hashing.murmur3_128();

    public <KeyType> String chooseNode(Set<String> nodeIds, byte[] key) {
        if (nodeIds.isEmpty()) {
            return null;
        }

        final HashCode keyHash = HASH_FN.hashBytes(key);
        long maxHash = Long.MIN_VALUE;
        String maxNode = null;

        for (String nodeId : nodeIds) {
            HashCode nodeHash = HASH_FN.hashString(nodeId, StandardCharsets.UTF_8);
            List<HashCode> hashes = Lists.newArrayList(nodeHash, keyHash);
            long combinedHash = Hashing.combineOrdered(hashes).asLong();
            if (maxNode == null) {
                maxHash = combinedHash;
                maxNode = nodeId;
            } else if (combinedHash > maxHash) {
                maxHash = combinedHash;
                maxNode = nodeId;
            }
        }

        return maxNode;
    }
}