In a pessimistic cache, if a transaction T1 has a put(k, v) operation and the primary owner of the key is the originator, the lock is acquired on the originator but it is not replicated to on the backup(s).

If one of the backup owners becomes the primary owner, it will allow another transaction T2 to lock (and update) key k before it receives the one-phase prepare command from the originator of T1.