OOM: OOM command not allowed when used memory > 'maxmemory'

What does it mean?

Memory used by Redis has reached the maxmemory limit and write commands are rejected because the eviction policy cannot free space for new data. Memory is full; writes are not possible.

Why does it happen?

The maxmemory limit is exceeded, the noeviction policy is selected (no key is ever removed), data without TTL keeps growing, a memory leak, or insufficient RAM for the limit.

How to fix it

Inspect memory usage: INFO memory and MEMORY USAGE. Choose an appropriate eviction policy (e.g. allkeys-lru or volatile-lru): CONFIG SET maxmemory-policy allkeys-lru. Set TTLs on keys so they are cleaned up automatically. Increase maxmemory/RAM. Find and shrink big keys (redis-cli --bigkeys). Purge unnecessary data.