How to lock a redis

redis locking classification

The locking commands that can be used by redis are INCR, SETNX, and SET.

1. The first lock command INCR

The idea of ​​​​this kind of locking is that if the key does not exist, then the value of the key will be initialized to 0 first, and then the INCR operation will be performed to add it. one.
Then when other users perform the INCR operation to add one, if the number returned is greater than 1, it means that the lock is being used.

1. Client A requests the server to obtain the key value of 1, indicating that the lock has been obtained.

2. Client B also requests the server to obtain the key value of 2, indicating that the lock acquisition failed.

3. Client A completes the execution of the code and deletes the lock

4. Client B waits for a period of time and obtains the key value of 1 when making a request, indicating that the lock acquisition is successful

5. Client B executes the code and deletes the lock.

$redis->incr($key);
$redis->expire($key, $ttl); //设置生成时间为1秒

2. The second lock SETNX

The idea behind this lock is that if the key does not exist, set the key to value

If the key already exists, SETNX will not take any action

1. Client A requests the server to set the value of the key. If the setting is successful, it means the lock is successful

2. Client B also requests the server to set the key value. If the return fails, it means that the lock failed

3. Client A completes the code execution and deletes the lock

4. Client After waiting for a period of time, client B requests to set the key value, and the setting is successful

5. Client B completes the code execution and deletes the lock

$redis->setNX($key, $value);
$redis->expire($key, $ttl);

3. The third type of lock SET

There is a problem with the above two methods. You will find that you need to set the key expiration. So why do we need to set key expiration? If the request execution exits unexpectedly for some reason, causing the lock to be created but not deleted, then the lock will always exist, so that the cache will never be updated in the future. So we need to add an expiration time to the lock to prevent unexpected events.

But setting it with Expire is not an atomic operation. Therefore, atomicity can also be ensured through transactions, but there are still some problems, so the official cited another one. The use of the SET command itself has included the function of setting the expiration time starting from version 2.6.12.

1. Client A requests the server to set the key value. If the setting is successful, the lock is successful.

2. Client B also requests the server to set the key value. If the return fails, Then it means that the lock failed

3. Client A completes the execution of the code and deletes the lock

4. Client B requests to set the key value after waiting for a period of time, and the setting is successful

5. Client B executes the code and deletes the lock

 $redis->set($key, $value, array('nx', 'ex' => $ttl)); //ex表示秒

For more Redis related knowledge, please visit the Redis usage tutorial column!

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