What are some examples of pessimistic locking in databases?

What are some examples of pessimistic locking in databases?

Pessimistic locking is a concurrency control mechanism where a transaction locks a resource to prevent others from accessing it. For example, in a banking application, when a user is transferring money, the account balance might be locked to prevent other transactions from modifying it until the transfer is complete.

Can you give me a specific scenario where this is useful?

Sure! Imagine a scenario in an online ticket booking system. When a user selects tickets for a concert, the system can apply a pessimistic lock on those tickets to ensure that no one else can book them until the user completes the transaction or cancels it.

What are the downsides of using pessimistic locking?

The main downsides include reduced concurrency, as other transactions must wait for the lock to be released, which can lead to performance bottlenecks. Additionally, it can increase the risk of deadlocks if not managed properly.

Are there alternatives to pessimistic locking?

Yes, alternatives include optimistic locking, where transactions proceed without locking resources and check for conflicts before committing, and using versioning to manage concurrent access.