简介

Redis集群将所有的存储空间分成了16384个槽（0~16383），每个主节点保存其中一部分槽。对某个键key操作时，先通过计算（CRC16（key）&16383）找到对应的槽，再把请求重定向到对应的节点上处理。

代码

public class RedisClusterUtil {
    
    /**
     * 计算键对应的槽
     *
     * @param key
     * @return
     */
    public static int getSlot(String key) {
        // 若键中有哈希标签（被左大括号和右大括号包裹的部分），则只有哈希标签会被计算
        key = key.contains("{") && key.contains("}") ? key.substring(key.indexOf("{") + 1, key.indexOf("}")) : key;
        // Redis集群有16384个槽（0-16383）
        return crc16(key) & 16383;
    }

    /**
     * CRC16算法
     *
     * @param key
     * @return
     */
    private static int crc16(String key) {
        int crc = 0;
        for (int i = 0; i < key.length(); i++) {
            crc = (crc << 8) ^ crc16Tab[((crc >> 8) ^ key.charAt(i)) & 0x00FF];
        }
        return crc;
    }

    /**
     * 查表法，提高效率
     */
    private static int[] crc16Tab =
            {
                    0x0000, 0x1021, 0x2042, 0x3063, 0x4084, 0x50a5, 0x60c6, 0x70e7,
                    0x8108, 0x9129, 0xa14a, 0xb16b, 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef,
                    0x1231, 0x0210, 0x3273, 0x2252, 0x52b5, 0x4294, 0x72f7, 0x62d6,
                    0x9339, 0x8318, 0xb37b, 0xa35a, 0xd3bd, 0xc39c, 0xf3ff, 0xe3de,
                    0x2462, 0x3443, 0x0420, 0x1401, 0x64e6, 0x74c7, 0x44a4, 0x5485,
                    0xa56a, 0xb54b, 0x8528, 0x9509, 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d,
                    0x3653, 0x2672, 0x1611, 0x0630, 0x76d7, 0x66f6, 0x5695, 0x46b4,
                    0xb75b, 0xa77a, 0x9719, 0x8738, 0xf7df, 0xe7fe, 0xd79d, 0xc7bc,
                    0x48c4, 0x58e5, 0x6886, 0x78a7, 0x0840, 0x1861, 0x2802, 0x3823,
                    0xc9cc, 0xd9ed, 0xe98e, 0xf9af, 0x8948, 0x9969, 0xa90a, 0xb92b,
                    0x5af5, 0x4ad4, 0x7ab7, 0x6a96, 0x1a71, 0x0a50, 0x3a33, 0x2a12,
                    0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, 0x9b79, 0x8b58, 0xbb3b, 0xab1a,
                    0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, 0x2c22, 0x3c03, 0x0c60, 0x1c41,
                    0xedae, 0xfd8f, 0xcdec, 0xddcd, 0xad2a, 0xbd0b, 0x8d68, 0x9d49,
                    0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, 0x3e13, 0x2e32, 0x1e51, 0x0e70,
                    0xff9f, 0xefbe, 0xdfdd, 0xcffc, 0xbf1b, 0xaf3a, 0x9f59, 0x8f78,
                    0x9188, 0x81a9, 0xb1ca, 0xa1eb, 0xd10c, 0xc12d, 0xf14e, 0xe16f,
                    0x1080, 0x00a1, 0x30c2, 0x20e3, 0x5004, 0x4025, 0x7046, 0x6067,
                    0x83b9, 0x9398, 0xa3fb, 0xb3da, 0xc33d, 0xd31c, 0xe37f, 0xf35e,
                    0x02b1, 0x1290, 0x22f3, 0x32d2, 0x4235, 0x5214, 0x6277, 0x7256,
                    0xb5ea, 0xa5cb, 0x95a8, 0x8589, 0xf56e, 0xe54f, 0xd52c, 0xc50d,
                    0x34e2, 0x24c3, 0x14a0, 0x0481, 0x7466, 0x6447, 0x5424, 0x4405,
                    0xa7db, 0xb7fa, 0x8799, 0x97b8, 0xe75f, 0xf77e, 0xc71d, 0xd73c,
                    0x26d3, 0x36f2, 0x0691, 0x16b0, 0x6657, 0x7676, 0x4615, 0x5634,
                    0xd94c, 0xc96d, 0xf90e, 0xe92f, 0x99c8, 0x89e9, 0xb98a, 0xa9ab,
                    0x5844, 0x4865, 0x7806, 0x6827, 0x18c0, 0x08e1, 0x3882, 0x28a3,
                    0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a,
                    0x4a75, 0x5a54, 0x6a37, 0x7a16, 0x0af1, 0x1ad0, 0x2ab3, 0x3a92,
                    0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, 0xbdaa, 0xad8b, 0x9de8, 0x8dc9,
                    0x7c26, 0x6c07, 0x5c64, 0x4c45, 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1,
                    0xef1f, 0xff3e, 0xcf5d, 0xdf7c, 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8,
                    0x6e17, 0x7e36, 0x4e55, 0x5e74, 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0
            };
}

测试

    public static void main(String[] args) {
        String[] keys = {"a", "b", "c", "d", "e", "{a}001", "{a}002"};
        for (int i = 0; i < keys.length; i++) {
            String key = keys[i];
            System.out.printf("key：%s 被分配到的槽为：%d\n", key, RedisClusterUtil.getSlot(key));
        }
    }

输出结果：

key：a 被分配到的槽为：15495
key：b 被分配到的槽为：3300
key：c 被分配到的槽为：7365
key：d 被分配到的槽为：11298
key：e 被分配到的槽为：15363
key：{a}001 被分配到的槽为：15495
key：{a}002 被分配到的槽为：15495

用redis客户端验证：

192.168.1.201:6380> cluster keyslot a
(integer) 15495
192.168.1.201:6380> cluster keyslot b
(integer) 3300
192.168.1.201:6380> cluster keyslot c
(integer) 7365
192.168.1.201:6380> cluster keyslot d
(integer) 11298
192.168.1.201:6380> cluster keyslot e
(integer) 15363
192.168.1.201:6380> cluster keyslot {a}001
(integer) 15495
192.168.1.201:6380> cluster keyslot {a}002
(integer) 15495