3.8 Eviction Policies

With the default configuration, a Redis instance that fills its memory does not delete anything. Its default eviction policy is noeviction, so once the configured limit is reached, every write that needs more memory fails with an error while reads keep working. For a cache, that is usually the wrong behavior, and choosing the right policy is the subject of this lesson.

When memory reaches the limit, Redis either refuses new writes or deletes keys to make room. The eviction policy decides which keys it deletes, and the amount of memory you provide decides how often that happens