Can you explain the difference between optimistic and pessimistic locking? In what scenarios would you employ each?

Optimistic locking is a strategy that allows transactions to execute without locking resources, checking for conflicts only before committing. It’s best used in scenarios with low contention for resources. Pessimistic locking, on the other hand, locks the resource from the start, preventing other transactions from accessing it. It's suitable for high contention situations where conflicts are likely to occur.