Expiration mechanism of ApsaraDB for Memcache is as follows.
Each key expires at a user-defined time. After expiration, the key becomes inaccessible. The space occupied by the expired key is not recycled immediately after expiration, but is recycled at 02:00 every day. In historical monitoring data, cached records include expired records. ItemCount decreases sharply at 02:00 when expired records are cleared.