Understanding Redis Memory Eviction: 6 Policies Explained
When Redis reaches its maxmemory limit, it can use one of six eviction policies—volatile‑lru, allkeys‑lru, volatile‑random, allkeys‑random, volatile‑ttl, or noeviction—to decide which keys to remove, with defaults and configurable sampling influencing performance and accuracy.
When Redis's maximum usable memory is exhausted, it follows one of six configurable eviction policies.
volatile-lru : Uses the LRU algorithm to delete keys that have an expiration set.
allkeys-lru : Uses the LRU algorithm to delete any key, regardless of expiration.
volatile-random : Randomly deletes keys with an expiration set.
allkeys-random : Randomly deletes any key.
volatile-ttl : Deletes the key with the nearest expiration among keys that have an expiration set.
noeviction : Does not evict; write operations that exceed memory return an error.
The default policy is noeviction , configured via maxmemory-policy .
For LRU‑based policies, Redis samples a small number of keys (default 5 ) and evicts the least recently used among them. The sample size is set by maxmemory-samples and can be adjusted; larger samples improve accuracy but increase CPU usage, while smaller samples are faster but less precise.
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