How to lock redis

This article mainly introduces several methods of locking in redis, and shares them for your reference and study. I won’t say much below, let’s take a look at the detailed introduction.

redis lock classification

The locking command tables that can be used by redis are INCR, SETNX, and SET

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 executed. The INCR operation adds 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

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 B waits for a period of time before requesting 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);

Third Seed lock SET

The above two methods have a problem. You will find that they 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 accidents.

But using Expire to set it 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. Using 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 completes the code execution and deletes the lock

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

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