Talking about redis’ Transaction Operations

  redis

Order

This article mainly studies the transaction operation of redis

Command

Multi and exec

  • command line
127.0.0.1:6379> multi
OK
127.0.0.1:6379> incr total
QUEUED
127.0.0.1:6379> incr len
QUEUED
127.0.0.1:6379> exec
1) (integer) 2
2) (integer) 2
127.0.0.1:6379> get total
"2"
127.0.0.1:6379> get len
"2"
  • Lettuce instance
    @Test
    public void testMultiExec(){
        RedisClient client = RedisClient.create("redis://192.168.99.100:6379/0");
        StatefulRedisConnection<String, String> connection = client.connect();
        RedisCommands<String, String> syncCommands = connection.sync();

        syncCommands.set("hello","1");
        syncCommands.set("world","2");

        syncCommands.multi();
        syncCommands.incr("hello");
        syncCommands.incr("world");

        //DefaultTransactionResult[wasRolledBack=false,result=[1, 2, 1, 3, 1]]
        TransactionResult transactionResult = syncCommands.exec();
        System.out.println(transactionResult);
        System.out.println(syncCommands.get("hello"));
        System.out.println(syncCommands.get("world"));
    }

Partial execution

  • command line
127.0.0.1:6379> multi
OK
127.0.0.1:6379> set a hello
QUEUED
127.0.0.1:6379> set b world
QUEUED
127.0.0.1:6379> incr a
QUEUED
127.0.0.1:6379> set c part
QUEUED
127.0.0.1:6379> exec
1) OK
2) OK
3) (error) ERR value is not an integer or out of range
4) OK
127.0.0.1:6379> get a
"hello"
127.0.0.1:6379> get b
"world"
127.0.0.1:6379> get c
"part"
  • Lettuce instance
    @Test
    public void testMultiExecError(){
        RedisClient client = RedisClient.create("redis://192.168.99.100:6379/0");
        StatefulRedisConnection<String, String> connection = client.connect();
        RedisCommands<String, String> syncCommands = connection.sync();

        syncCommands.multi();
        syncCommands.set("a","hello");
        syncCommands.set("b","world");
        syncCommands.incr("a");
        syncCommands.set("c","part");
        //DefaultTransactionResult[wasRolledBack=false,result=[OK, OK, io.lettuce.core.RedisCommandExecutionException: ERR value is not an integer or out of range, OK, 1]]
        TransactionResult transactionResult = syncCommands.exec();
        System.out.println(transactionResult);
        System.out.println(syncCommands.get("a"));
        System.out.println(syncCommands.get("b"));
        System.out.println(syncCommands.get("c"));
    }

Multi and discard

  • command line
127.0.0.1:6379> set sum 1
OK
127.0.0.1:6379> multi
OK
127.0.0.1:6379> incr sum
QUEUED
127.0.0.1:6379> discard
OK
127.0.0.1:6379> get sum
"1"
  • Lettuce instance
    @Test
    public void testMultiDiscard(){
        RedisClient client = RedisClient.create("redis://192.168.99.100:6379/0");
        StatefulRedisConnection<String, String> connection = client.connect();
        RedisCommands<String, String> syncCommands = connection.sync();
        syncCommands.incr("key1");
        syncCommands.multi();
        syncCommands.incr("key1");
        //需要有multi才可以执行discard,成功返回OK
        String result = syncCommands.discard();
        System.out.println(result);
        System.out.println(syncCommands.get("key1"));
    }

check and set

    @Test
    public void testWatch(){
        RedisClient client = RedisClient.create("redis://192.168.99.100:6379/0");
        StatefulRedisConnection<String, String> connection = client.connect();
        RedisCommands<String, String> syncCommands = connection.sync();

        String key = "key";
        syncCommands.watch(key);

        //another connection
        StatefulRedisConnection<String, String> conn2 = client.connect();
        RedisCommands<String, String> syncCommands2 = conn2.sync();
        syncCommands2.set(key, "a");

        syncCommands.multi();
        syncCommands.append(key, "b");
        //DefaultTransactionResult [wasRolledBack=true, responses=0]
        TransactionResult transactionResult = syncCommands.exec();
        System.out.println(transactionResult);

        System.out.println(syncCommands.get(key));
    }

Summary

  • Reids provides multi exec/discard instructions, similar to open commit/rollback transaction, but exec will not roll when encountering errors such as type operations. the successfully executed command is still successfully executed, and the failed command is still failed
  • Multi exec guarantees that as long as exec command is executed successfully, a series of commands in the transaction can be executed. if exec is not received by server due to network problems, a series of commands in the transaction will not be executed.
  • Discard can only be used if multi is called. This command will empty the transaction queue of commands waiting to be executed.
  • Redis provides the watch instruction, which can be used in conjunction with multi exec, and can implement a mechanism similar to the optimistic locking of a database. once the watch key is updated by other client, the entire exec operation fails

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