LUA

Lua是作為嵌入式指令碼的最佳選擇,速度非常快

在redis命令列中，可以直接呼叫lua指令碼，比如

127.0.0.1:6380> eval "local result={}  for loop=1, #(KEYS) do result[loop]=redis.call('hget',KEYS[loop], ARGV[1]) end return result" 3 xiaoa xiaob xiaoc count

1) "2"
2) "5"
3) "1"
127.0.0.1:6380>

使用SpringBoot呼叫lua指令碼，存在兩種方式

一、直接在程式碼中通過字串呼叫

        StringBuilder lua = new
 
 StringBuilder();
        lua.append("local result={} ");
        lua.append("for loop=1, #(KEYS) ");
        lua.append("do result[loop]=redis.call('hget',KEYS[loop], ARGV[1]) ");
        lua.append("end ");
        lua.append("return result");

        RedisScript<List> script = RedisScript.of(lua.toString(), List.class
 
);

        List<String> keys = new ArrayList<String>();
        keys.add("xiaoa");
        keys.add("xiaob");
        keys.add("xiaoc");

        List<Object> args = new ArrayList<>();
        args.add("count");

        List<String> result = redisTemplate.execute(script, keys, args.toArray());

        logger.info(
 
"luaTest: {}", result);

二、通過lua指令碼檔案呼叫

1、指令碼檔案，count_qry.lua

local result={}
  for loop = 1,#(KEYS)
      do result[loop]= redis.call('hget',KEYS[loop], ARGV[1])
  end
return result

        // src/main/resources下
        ClassPathResource resource = new ClassPathResource("lua/count_qry.lua");
        RedisScript<List> script = RedisScript.of(resource, List.class);

        List<String> keys = new ArrayList<String>();
        keys.add("xiaoa");
        keys.add("xiaob");
        keys.add("xiaoc");

        List<Object> args = new ArrayList<>();
        args.add("count");

        List<String> result = redisTemplate.execute(script, keys, args.toArray());

        logger.info("luaFileTest: {}", result);

使用springboot pipeline也能實現上述的功能

        List<Object> result = redisTemplate.executePipelined(new RedisCallback() {

            @Override
            public List<String> doInRedis(RedisConnection connection) throws DataAccessException {
                List<String> keys = new ArrayList<String>();
                keys.add("xiaoa");
                keys.add("xiaob");
                keys.add("xiaoc");

                for (int i = 0; i < keys.size(); i++) {
                    connection.hGet(keys.get(i).getBytes(), "count".getBytes());
                }
                // 必須返回null，否則將出現異常
                return null;
            }
        });

        logger.info("result: {}", result);

使用lua指令碼和pipeline都可以實現簡單的原子性，但lua指令碼比pipelin更靈活，實現功能更多，比如有個佇列，存放的資料不能超過N個，超過的將不會被儲存，這種實現方式很多，其中一種方式比如在插入佇列資料之前，先查詢下資料個數，大於等於N個，則不新增，這個邏輯用pipeline不能夠實現，但可以用lua實現，假設N=3

local len=redis.call('llen',KEYS[1])
if len >= 3
    then return false
else
    redis.call('lpush',KEYS[1],ARGV[1])
    return true
end

        // src/main/resources下
        ClassPathResource resource = new ClassPathResource("lua/queue.lua");
        RedisScript<Boolean> script = RedisScript.of(resource, Boolean.class);

        List<String> keys = new ArrayList<String>();
        keys.add("testqueue");
        List<Object> args = new ArrayList<>();
        args.add("val");

        for (int i = 0; i < 4; i++) {
            boolean result = redisTemplate.execute(script, keys, args.toArray());
            logger.info("add val to queue result: {}", result);
        }

結果，前三個資料成功插入，第四個資料被拒絕

2021-12-24 15:29:36.961  INFO 34276 --- [           main] com.demo.redistest.RedisLuaTest          : add val to queue result: true
2021-12-24 15:29:36.964  INFO 34276 --- [           main] com.demo.redistest.RedisLuaTest          : add val to queue result: true
2021-12-24 15:29:36.966  INFO 34276 --- [           main] com.demo.redistest.RedisLuaTest          : add val to queue result: true
2021-12-24 15:29:36.968  INFO 34276 --- [           main] com.demo.redistest.RedisLuaTest          : add val to queue result: false