10.3.2. About Pessimistic Locking
Pessimistic locking is also known as eager locking.
Pessimistic locking prevents more than one transaction being written to a key by enforcing cluster-wide locks on each write operation. Locks are only released once the transaction is completed either through committing or being rolled back.
Pessimistic mode is used where a high contention on keys is occurring, resulting in inefficiencies and unexpected roll back operations.