All 7 Expiration & Eviction questions
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 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 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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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?

Intermediate

Answer

You check the evicted_keys statistic available through the INFO command, and a consistently rising number of evictions can indicate your Redis instance does not have enough memory for your workload, which is important to monitor since unexpected evictions of data your application still needs can lead to increased load on your backing database or degraded user experience.
redis-cli info stats | grep evicted_keys
Real-world example A team notices a steadily increasing eviction count in their monitoring dashboard, prompting them to either increase their Redis instance's available memory or investigate why so much data is being stored that does not truly need to remain cached.

Common follow-ups: What is a healthy or expected eviction rate for a typical caching workload?;How do you set up an alert for when evictions start increasing unexpectedly?

Redis Monitoring & Observability;Redis Memory Optimization
All 7 Expiration & Eviction questions