Redis Transactions

Redis provides support for transactions through the multi, exec, and discard commands. These operations are available on RedisTemplate. However, RedisTemplate is not guaranteed to run all the operations in the transaction with the same connection.spring-doc.cn

Spring Data Redis provides the SessionCallback interface for use when multiple operations need to be performed with the same connection, such as when using Redis transactions.The following example uses the multi method:spring-doc.cn

//execute a transaction
List<Object> txResults = redisOperations.execute(new SessionCallback<List<Object>>() {
  public List<Object> execute(RedisOperations operations) throws DataAccessException {
    operations.multi();
    operations.opsForSet().add("key", "value1");

    // This will contain the results of all operations in the transaction
    return operations.exec();
  }
});
System.out.println("Number of items added to set: " + txResults.get(0));

RedisTemplate uses its value, hash key, and hash value serializers to deserialize all results of exec before returning. There is an additional exec method that lets you pass a custom serializer for transaction results.spring-doc.cn

It is worth mentioning that in case between multi() and exec() an exception happens (e.g. a timeout exception in case Redis does not respond within the timeout) then the connection may get stuck in a transactional state. To prevent such a situation need have to discard the transactional state to clear the connection:spring-doc.cn

List<Object> txResults = redisOperations.execute(new SessionCallback<List<Object>>() {
  public List<Object> execute(RedisOperations operations) throws DataAccessException {
    boolean transactionStateIsActive = true;
	try {
      operations.multi();
      operations.opsForSet().add("key", "value1");

      // This will contain the results of all operations in the transaction
      return operations.exec();
    } catch (RuntimeException e) {
	    operations.discard();
		throw e;
    }
  }
});

@Transactional Support

By default, RedisTemplate does not participate in managed Spring transactions. If you want RedisTemplate to make use of Redis transaction when using @Transactional or TransactionTemplate, you need to be explicitly enable transaction support for each RedisTemplate by setting setEnableTransactionSupport(true). Enabling transaction support binds RedisConnection to the current transaction backed by a ThreadLocal. If the transaction finishes without errors, the Redis transaction gets commited with EXEC, otherwise rolled back with DISCARD. Redis transactions are batch-oriented. Commands issued during an ongoing transaction are queued and only applied when committing the transaction.spring-doc.cn

Spring Data Redis distinguishes between read-only and write commands in an ongoing transaction. Read-only commands, such as KEYS, are piped to a fresh (non-thread-bound) RedisConnection to allow reads. Write commands are queued by RedisTemplate and applied upon commit.spring-doc.cn

The following example shows how to configure transaction management:spring-doc.cn

Example 1. Configuration enabling Transaction Management
@Configuration
@EnableTransactionManagement                                 (1)
public class RedisTxContextConfiguration {

  @Bean
  public StringRedisTemplate redisTemplate() {
    StringRedisTemplate template = new StringRedisTemplate(redisConnectionFactory());
    // explicitly enable transaction support
    template.setEnableTransactionSupport(true);              (2)
    return template;
  }

  @Bean
  public RedisConnectionFactory redisConnectionFactory() {
    // jedis || Lettuce
  }

  @Bean
  public PlatformTransactionManager transactionManager() throws SQLException {
    return new DataSourceTransactionManager(dataSource());   (3)
  }

  @Bean
  public DataSource dataSource() throws SQLException {
    // ...
  }
}
1 Configures a Spring Context to enable declarative transaction management.
2 Configures RedisTemplate to participate in transactions by binding connections to the current thread.
3 Transaction management requires a PlatformTransactionManager. Spring Data Redis does not ship with a PlatformTransactionManager implementation. Assuming your application uses JDBC, Spring Data Redis can participate in transactions by using existing transaction managers.

The following examples each demonstrate a usage constraint:spring-doc.cn

Example 2. Usage Constraints
// must be performed on thread-bound connection
template.opsForValue().set("thing1", "thing2");

// read operation must be run on a free (not transaction-aware) connection
template.keys("*");

// returns null as values set within a transaction are not visible
template.opsForValue().get("thing1");