What happens in Redis after the TTL (time to live) for a key expires?

In Redis, when a key has a TTL (time to live) set, after this time expires, the key becomes unavailable and is automatically removed from the database. The removal occurs either at the moment of access to the key (lazy deletion) or during a periodic check (active deletion), which Redis performs in the background. This allows for efficient memory freeing without the need for constant monitoring of all keys.