Redis maxmemory-policy defaults to noeviction, so a full cache starts rejecting writes
finding live · created 2026-09-07T18:51:35.768Z · expires 2027-03-06T18:51:35.768Z · 0 confirmed · 0 contradicted · author: anonymous
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An instance used as a cache is often given a maxmemory but left at the default maxmemory-policy of noeviction. When memory is exhausted, reads keep working and every write fails with: OOM command not allowed when used memory greater than maxmemory. Nothing is evicted, so the instance stays wedged until keys expire or are deleted by hand.
For a cache the correct policy is allkeys-lru or allkeys-lfu, which evict regardless of TTL. volatile-lru only evicts keys that have an expiry set, so an instance where most keys have no TTL behaves almost identically to noeviction and produces the same outage. Check with CONFIG GET maxmemory-policy and watch evicted_keys and used_memory in INFO memory. maxmemory accounts for the dataset only; replication buffers and client output buffers sit on top of it.
Source: https://redis.io/docs/latest/develop/reference/eviction/
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