Shulou(Shulou.com)06/01 Report--

Redis Watch Command

Function:

Used to monitor a key (or keys), if the key (or keys) is changed by another command before the transaction executes, then the transaction will be interrupted.

Usage:

redis 127.0.0.1:6379> WATCH key1 key2

OK

Redis Unwatch Command

Function:

Used to cancel the WATCH command to monitor all keys.

Usage:

redis 127.0.0.1:6379> UNWATCH

OK

Redis Multi command

Function:

Used to mark the beginning of a transaction block. Multiple commands within a transaction block are placed in a queue in sequential order, and finally executed atomically by the EXEC command.

Usage:

redis 127.0.0.1:6379> MULTI #Mark transaction start OKredis 127.0.0.1: 6379> INCR user_id #Multiple commands enqueue sequentially QUEUEDredis 127.0.0.1: 6379> INCR user_idQUEUEDredis 127.0.0.1: 6379> INCR user_idQUEUEDredis 127.0.0.1: 6379> PINGQUEUEDredis 127.0.0.1: 6379> EXEC #execute 1) (integer) 12) (integer) 23) (integer) 34) PONG

Using watch to implement incr

This is done as follows:

WATCH mykey val = GET mykey val = val + 1 MULTI SET mykey $val EXEC

Monitoring mykey by WATCH command before getting the value of mykey, and then wrapping set command in transaction, can effectively ensure that each connection before executing EXEC, if the mykey value obtained by the current connection is modified by the client of other connections, then the EXEC command of the current connection will fail. This way the caller can tell if val was reset successfully after judging the return value.

Attention:

·Since the WATCH command only prevents the execution of a transaction after the monitored key has been modified, it cannot guarantee that other clients will not modify the key, so in general we need to re-execute the entire function after EXEC fails.

EXEC command will cancel the monitoring of all keys, if you do not want to execute the command in the transaction can also use UNWATCH command to cancel the monitoring.

Examples:

Open two redis-cli command line windows, session 1 and session 2.

session 1:redis 127.0.0.1: 6379> set test 1 #Set test="1"OKredis 127.0.0.1: 6379> get test #Get the value of test as "1""1"redis 127.0.0.1: 6379> watch test #Monitor testOKredis 127.0.0.1: 6379> multi #Open transaction OKredis 127.0.0.1: 6379> set test 2 #Set test to "2"QUEUEDredis 127.0.0.1: 6379> exec #After session 2 is executed, execute the exec command of session 1, and find that the execution fails (nil)redis 127.0.0.1: 6379> get test #Get the value of test and find that the test value is "3""3"redis 127.0.0.1: 6379> unwatch set in session 2 #Unmonitor all keyOKredis 127.0.0.1: 6379> set test 4 #Non-transactional change test value is "4"OKredis 127.0.0.1: 6379> get test #Get test="4""4"session 2: redis 127.0.0.1: 6379> get test #Get test created by session 1 ="1""1"redis 127.0.0.1: 6379> watch test #Monitor testOKredis 127.0.0.1: 6379> multi #Open transaction OKredis 127.0.0.1: 6379> set test 3 #Set test to "3"QUEUEDredis 127.0.0.1: 6379> exec #Execute transaction 1) OKredis 127.0.0.1: 6379> get test #Get test="3""3"

summary

The above is the watch, multi and other commands involved in Redis affairs introduced by Xiaobian to you. I hope it will help you. If you have any questions, please leave a message to me. Xiaobian will reply to you in time. Thank you very much for your support!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.