:Retry mechanisms for Tair clients

Causes for temporary faults

Recommended retry rules

Jedis

We recommend that you use Jedis 4.0.0 or later, preferably the latest Jedis version. In the following example, Jedis 5.0.0 is used.

1. Add the following dependency to your pom.xml file to include Jedis:

       <dependency>
           <groupId>redis.clients</groupId>
           <artifactId>jedis</artifactId>
           <version>5.0.0</version>
       </dependency>

2. Use Jedis to retry a Tair operation.

   • If the instance is a standard instance or a cluster instance in proxy mode, you must use the JedisPool mode.

     The following sample code automatically retries the SET command up to 5 times within a total retry duration of 10 seconds, with exponentially increasing wait times between each retry. If all retries fail, an exception is thrown.

     PooledConnectionProvider provider = new PooledConnectionProvider(HostAndPort.from("127.0.0.1:6379"));
     int maxAttempts = 5; // The maximum number of retries.
     Duration maxTotalRetriesDuration = Duration.ofSeconds(10); // The maximum total retry duration.
     UnifiedJedis jedis = new UnifiedJedis(provider, maxAttempts, maxTotalRetriesDuration);
     try {
         System.out.println("set key: " + jedis.set("key", "value"));
     } catch (Exception e) {
         // If the exception is caught in this block, it implies that the operation failed even after the maximum number of attempts (maxAttempts) or after the maximum total retry duration (maxTotalRetriesDuration) is reached. 
         e.printStackTrace();
     }

   • If the instance is a cluster instance in direct connection mode, you must use the JedisCluster mode.

     You can configure the maxAttempts parameter to define the number of retry attempts in case of failure, with a default value of 5. If the operation is still unsuccessful after the maximum number of attempts, an exception is thrown.

     HostAndPort hostAndPort = HostAndPort.from("127.0.0.1:30001");
     int connectionTimeout = 5000;
     int soTimeout = 2000;
     int maxAttempts = 5;
     ConnectionPoolConfig config = new ConnectionPoolConfig();
     JedisCluster jedisCluster = new JedisCluster(hostAndPort, connectionTimeout, soTimeout, maxAttempts, config);
     try {
         System.out.println("set key: " + jedisCluster.set("key", "value"));
     } catch (Exception e) {
         // If the exception is caught in this block, it implies that the operation failed even after the maximum number of attempts (maxAttempts). 
         e.printStackTrace();
     }

Redisson

The Redisson client provides two parameters to control the retry logic:

• retryAttempts: the number of retries. Default value: 3.

• retryInterval: the retry interval. Default value: 1500. Unit: milliseconds.

Example of retry settings on the Jedis client:

Config config = new Config();
config.useSingleServer()
    .setTimeout(1000)
    .setRetryAttempts(3)
    .setRetryInterval(1500) //ms
    .setAddress("redis://127.0.0.1:6379");
RedissonClient connect = Redisson.create(config);

StackExchange.Redis

The StackExchang.Redis client supports only connection retries. Example of retry settings on the StackExchange.Redis client:

var conn = ConnectionMultiplexer.Connect("redis0:6380,redis1:6380,connectRetry=3");

Lettuce

Although the Lettuce client does not provide parameters for retries after a command times out, you can use the following parameters to implement a retry mechanism:

• at-most-once execution: The command can be executed once at most. If the client is disconnected and then reconnected, the command may be lost.

• at-least-once execution (default): A minimum of one successful command execution is ensured. This indicates that multiple attempts may be made to ensure a successful execution. If this method is used and a master/replica switchover occurs in the Tair instance while the client is making multiple retry attempts, a large number of retry commands may be accumulated on the client. After the master/replica switchover is complete, the CPU utilization of the Tair instance may surge.

Example of retry settings on the Lettuce client:

clientOptions.isAutoReconnect() ? Reliability.AT_LEAST_ONCE : Reliability.AT_MOST_ONCE;