All 7 Distributed Locks with Redis questions
More in Distributed Locks with Redis
What is a distributed lock, and why would an application need one when using Redis? Why is it important to release a distributed lock using a script that verifies you are actually the current lock owner, rather than a simple DELETE command? What happens if the process holding a distributed lock crashes or hangs before it finishes its work and releases the lock? What are some common mistakes developers make when implementing distributed locks with Redis, and how do you avoid them? What is the Redlock algorithm, and why was it proposed for implementing distributed locks across multiple independent Redis instances? How would you design a distributed lock implementation that supports safely extending the lock's expiration time if the protected operation needs more time than originally expected?
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How do you implement a basic distributed lock in Redis using the SET command with NX and EX options?

Beginner

Answer

You use the SET command with the NX option, which only sets the value if the key does not already exist, combined with the EX option to set an automatic expiration time, ensuring the lock is both exclusively acquired by only one client and automatically released after a timeout even if that client crashes before releasing it manually.
SET mylock 'unique_value_123' NX EX 30
-- If this returns OK, you have acquired the lock
-- If it returns nil, someone else already holds it
Real-world example A batch processing job attempts to acquire a lock before starting its work, and if the lock already exists because another instance is currently running, it simply skips its turn and tries again during its next scheduled run.

Common follow-ups: Why is it important to set a unique value rather than just a fixed string like 'locked'?;What happens if the operation protected by the lock takes longer than the expiration time?

Distributed Locks with Redis;Redis CLI & Basic Commands
All 7 Distributed Locks with Redis questions