一致性哈希：MurmurHash

功能：

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• hash 获取指定数据的一致性hash值

源码：

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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.
 */

import java.io.UnsupportedEncodingException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;

/**
 * This is a very fast, non-cryptographic hash suitable for general hash-based
 * lookup. See http://murmurhash.googlepages.com/ for more details.
 * <p/>
 * <p>
 * The C version of MurmurHash 2.0 found at that site was ported to Java by
 * Andrzej Bialecki (ab at getopt org).
 * </p>
 */
public class MurmurHash {
    
    private static final String UTF_8 = "UTF-8";

    public static long hash64A(byte[] data, int seed) {
        return hash64A(ByteBuffer.wrap(data), seed);
    }

    public static long hash64A(ByteBuffer buf, int seed) {
        ByteOrder byteOrder = buf.order();
        buf.order(ByteOrder.LITTLE_ENDIAN);

        long m = 0xc6a4a7935bd1e995L;
        int r = 47;

        long h = seed ^ (buf.remaining() * m);

        long k;
        while (buf.remaining() >= 8) {
            k = buf.getLong();

            k *= m;
            k ^= k >>> r;
            k *= m;

            h ^= k;
            h *= m;
        }

        if (buf.remaining() > 0) {
            ByteBuffer finish = ByteBuffer.allocate(8).order(ByteOrder.LITTLE_ENDIAN);
            // for big-endian version, do this first:
            // finish.position(8-buf.remaining());
            finish.put(buf).rewind();
            h ^= finish.getLong();
            h *= m;
        }

        h ^= h >>> r;
        h *= m;
        h ^= h >>> r;

        buf.order(byteOrder);
        return h;
    }

    public long hash(byte[] key) {
        return hash64A(key, 0x1234ABCD);
    }

    public long hash(String key) {
        return hash(encode(key));
    }

    private byte[] encode(String data) {
        try {
            return data.getBytes(UTF_8);
        } catch (UnsupportedEncodingException e) {
            throw new IllegalArgumentException(e);
        }
    }
}

用法：

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public static void main(String[] args) {
        // 根据uid做分库分表
        String uid = "09cd3de4a570dc31e86234d04afbca7d";
        
        MurmurHash hash = new MurmurHash();
        long h = hash.hash(uid) / 10;
        //long h = 2209705902952448L;
        
        // DB
        long dbIndex = (h & 255) >>> 4;
        System.out.println(dbIndex);
        
        // TABLE
        long tableIndex = h & 255;
        System.out.println(tableIndex);
    }