rediscluster lua使用

迷南。 2022-07-14 03:43 274阅读 0赞

redis中文网官方案例

redis 127.0.0.1:6379> eval "return {KEYS[1],KEYS[2],ARGV[1],ARGV[2]}" 2 key1 key2 first second
    1) "key1"
    2) "key2"
    3) "first"
    4) "second"

这在在单个redis中是可以成功的，在rediscluster中执行情况如下

redis 127.0.0.1:6379> eval "return {KEYS[1],KEYS[2],ARGV[1],ARGV[2]}" 2 key1 key2 first second
    (error) CROSSSLOT Keys in request don't hash to the same slot

会出现 CROSSSLOT Keys in request don’t hash to the same slot。  
原因是因为：Redis cluster对多key操作有限，要求命令中所有的key都属于一个slot，才可以被执行。  
想看jediscluster.eval()方法中获取getSlot()的实现

public T run(int keyCount, String... keys) {
        if (keys == null || keys.length == 0) {
          throw new JedisClusterException("No way to dispatch this command to Redis Cluster.");
        }
    
        // For multiple keys, only execute if they all share the
        // same connection slot.
        if (keys.length > 1) {
          int slot = JedisClusterCRC16.getSlot(keys[0]);
          for (int i = 1; i < keyCount; i++) {
            int nextSlot = JedisClusterCRC16.getSlot(keys[i]);
            if (slot != nextSlot) {
              throw new JedisClusterException("No way to dispatch this command to Redis Cluster "
                  + "because keys have different slots.");
            }
          }
        }

如果solt不一样会跑出异常，看获取getSolt()实现

public static int getSlot(String key) {  
      int s = key.indexOf("{");  
      if (s > -1) {  
        int e = key.indexOf("}", s + 1);  
        if (e > -1 && e != s + 1) {  
          key = key.substring(s + 1, e);  
        }  
      }  
      // optimization with modulo operator with power of 2 
      // equivalent to getCRC16(key) % 16384 
      return getCRC16(key) & (16384 - 1);  
    }

可以看出，keySlot算法中，如果key包含\{\}，就会使用第一个\{\}内部的字符串作为hash key，这样就可以保证拥有同样\{\}内部字符串的key就会拥有相同slot。

综上所述脚本改成

redis 127.0.0.1:6379> eval "return {KEYS[1],KEYS[2],ARGV[1],ARGV[2]}" 2 {key}1 {key}2 first second
    1) "{key}1"
    2) "{key}2"
    3) "first"
    4) "second"

执行成功。

lua使用：> [http://www.oschina.net/translate/intro-to-lua-for-redis-programmers][http_www.oschina.net_translate_intro-to-lua-for-redis-programmers]

[http_www.oschina.net_translate_intro-to-lua-for-redis-programmers]: http://www.oschina.net/translate/intro-to-lua-for-redis-programmers