What is the difference between pessimistic and optimistic locking?

[Jaiden]

Hi, I'd like to ask you something, what is the difference between pessimistic and optimistic locking? Please inform me please Help.

[Aadam]

- In pessimistic locking, when a user opens a data to update it, a lock is granted. Other users can only view the data until the whole transaction of the data update is completed.

- In optimistic locking, a data is opened for updating by multiple users. A lock is granted only during the update transaction and not for the entire session. Due to this concurrency is increased and is a practical approach of updating the data.