How is the redis lock implemented

Redis locks are implemented by leveraging Redis's SETNX and DEL atomic operations, as well as single-threaded execution characteristics. It implements locking by setting key-value pairs, unlocks using DEL delete keys, and sets expiration time to avoid deadlocks. Redis locks are simple and easy to use, high performance, and distributed, but relying on Redis, they have a risk of single point of failure, and lock timeout may lead to inconsistent data.

The implementation principle of Redis lock

Redis lock is a distributed lock that utilizes the atomic operation and single-thread execution characteristics of Redis.

Atomic operation

Redis's SETNX (SET if Not eXists) is an atomic operation that checks whether the key exists, sets the specified value to that key if it does not exist, and returns true, otherwise returns false.

Single threaded execution

All commands in Redis are executed single thread, which means that at a point in time, only one command will be executed.

Implementation principle

Based on the above characteristics, the implementation principle of Redis lock is as follows:

1. Locking:

   • Use the SETNX command to set a key with the name of the lock and the value is the current timestamp or other unique identifier.
   • If SETNX returns true, it means that the lock is successfully added and the process holds the lock.

2. Unlock:

   • Use the DEL command to delete the lock's key.
   • If the DEL command is successful, it means that the unlocking is successful.

3. Lock timeout:

   • Set the expiration time of a lock, and the lock will be automatically released after this time is exceeded. This can be achieved by using the EXPIRE command.

4. Avoid deadlocks:

   • To avoid deadlocks, a maximum time to hold the lock is usually introduced, and if this time has not been unlocked, other processes can force unlock.

Pros and cons

advantage:

• Simple and easy to use: The implementation principle of Redis lock is simple and easy to understand and easy to use.
• High Performance: Redis is a high performance database, so Redis locks also have high performance.
• Distributed: Redis locks are distributed and can be used on multiple Redis instances.

shortcoming:

• Reliables: Redis locks depend on the Redis database. If there is a problem with Redis, the lock will also fail.
• Single point of failure: If the Redis master node fails, the lock will also fail until the master node recovers.
• Lock timeout: Lock timeout may cause data inconsistency.

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