Redis Eviction Policy Not Working as Expected
If you're facing issues with Redis' eviction policy not working as expected, it's crucial to check the configuration and behavior of the maxmemory-policy setting.
Redis uses eviction policies to manage memory when the maxmemory setting is reached.
If the eviction policy isn’t behaving as expected, the first thing to verify is that maxmemory is set correctly in the Redis configuration.
If maxmemory isn’t set, Redis won’t evict any keys, and the server may run out of memory.
You can check the current memory usage and settings using the INFO memory command to see how much memory Redis is using and the current eviction policy.
Common eviction policies include noeviction, allkeys-lru, volatile-lru, allkeys-random, and volatile-random, but each policy has different behaviors.
The noeviction policy will not remove any keys, and instead, Redis will return an error if you try to insert more data.
The LRU (Least Recently Used) policies evict the least recently used keys, and the random policies remove keys at random from either all keys or only keys with an expiration set.
If your policy is not working as expected, it might be due to a misunderstanding of how the policies interact with key expiration.
For example, the volatile-lru policy only evicts keys with an expiration set, while allkeys-lru will evict any key.
Ensure that the correct policy is in place based on whether you want to prioritize eviction of keys with an expiration or all keys.
In cases where eviction seems ineffective, check if your application is interacting with Redis in a way that bypasses eviction policies, such as using SETNX, which prevents keys from being overwritten.
Additionally, confirm that your Redis version supports the eviction policy you're using, as older versions may have limitations.
If the issue persists, consider experimenting with a different eviction policy to see if another strategy works better for your use case.
In extreme cases, Redis may be under memory pressure and may not perform eviction as quickly as needed.
Monitoring the system with the INFO memory and CLIENT LIST commands can provide insight into whether Redis is under load or has memory bottlenecks.
Finally, ensure that your Redis instance has sufficient resources, such as CPU, disk space, and network bandwidth, to handle evictions under heavy load.
