What is the difference between optimistic and pessimistic locking?

[chinmay.sahoo]

Pessimistic is used when the user want to lock the records so that no one can update data. The user are only allowed to view the data.
In optimistic multiple user can update an view the data

[TomClarke]

As for pessimistic locking: on updаting the data, the record gets locked and no one else can access that record for updаting. It becomes a read-only record till the lick is released. Once the lock gets released, the record can be locked again and get updated for a different user.
And optimistic locking: this allows multiple user to open up the same record for updаting. Record gets locked only while updаting the record. This is the most preffered way of locking for the web application.