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What is the difference between the EXPIRE, TTL, and PERSIST commands in Redis? What eviction policies are available in Redis for handling the situation when memory usage reaches its configured maximum limit? What is the difference between the LRU and LFU eviction algorithms, and when would you choose one over the other? How do you monitor how many keys are currently being evicted from Redis due to memory pressure, and why is this an important metric to track? How would you diagnose and resolve a situation where important data is being unexpectedly evicted from Redis due to memory pressure? How does Redis actually implement key expiration internally, using both a passive and an active approach?
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Redis › Expiration & Eviction

How do you set an expiration time on a Redis key so it automatically gets deleted after a certain period?

Beginner

Answer

You can set an expiration time when creating a key using SET with the EX option for seconds or PX for milliseconds, or apply it to an already existing key using the EXPIRE command, after which Redis automatically removes the key once that time has passed without needing any manual cleanup.
SET session:abc123 'userdata' EX 3600
EXPIRE session:abc123 3600
Real-world example A web application stores a user's login session in Redis with a one hour expiration, automatically logging them out and cleaning up the session data without needing a separate scheduled cleanup process.

Common follow-ups: What happens if you set a new value on a key that already had an expiration set?;How do you check how much time is left before a key expires?

Session Management with Redis;Caching Patterns
All 7 Expiration & Eviction questions