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

What is the difference between the EXPIRE, TTL, and PERSIST commands in Redis?

Beginner

Answer

EXPIRE sets a countdown timer on a key after which it will be automatically deleted, TTL checks how much time remains before that countdown reaches zero, and PERSIST removes any existing expiration from a key, making it permanent again until explicitly deleted or given a new expiration.
EXPIRE mykey 60
TTL mykey -- returns remaining seconds
PERSIST mykey -- removes the expiration entirely
Real-world example A promotional discount code is given a temporary expiration using EXPIRE, checked periodically with TTL to show a countdown to customers, and made permanent using PERSIST if the promotion is later extended indefinitely.

Common follow-ups: What does TTL return if a key has no expiration set at all?;What does TTL return if the key does not exist at all?

Redis CLI & Basic Commands;Caching Patterns
All 7 Expiration & Eviction questions