Software Architect's Handbook

Optimistic versus pessimistic concurrency control

Concurrency control ensures that databases transactions that are performed concurrently maintain data integrity. Many databases offer two main types of concurrency control: optimistic and pessimistic.

Optimistic concurrency control (or optimistic locking) works under the assumption that resource conflicts between multiple users, while possible, are not common. Therefore, it allows transactions to execute without locking resources. If data is being changed, resources are checked for conflicts. If there is a conflict, only one transaction is successful while the others fail.

In contrast, pessimistic concurrency (or pessimistic locking) assumes the worst, such as assuming that more than one ...