Memory limit is reached and the client tries to execute commands that will allow more memory to be used (most write instructions, but DEL and a few exceptions)
Allkeys-lru: Attempts to reclaim the least-used key (LRU) to make room for newly added data.
Volatile – LRU: Attempts to reclaim the least-used key (LRU), but only the key in the expired set, so that newly added data has space to store.
Allkeys-random: Retrieves random keys to make room for newly added data.
Volatile -random: Retrievals random keys to make room for newly added data, but only for keys in expired collections.
Volatile – TTL: Retrievals the keys in the expired set, and prioritized the keys with a shorter TTL to make room for newly added data.