What is the difference between optimistic and pessimistic locking strategies in managing database concurrency?
sobes.tech AI
Answer from AI
Pessimistic and optimistic locking are two strategies for managing concurrent access to data in databases.
Pessimistic locking assumes that conflicts during concurrent data access are likely, so a transaction immediately acquires a lock on the data to prevent other transactions from modifying it until the current transaction completes. This prevents conflicts but can reduce concurrency and lead to blocking and deadlocks.
Optimistic locking assumes that conflicts are rare. The transaction does not lock data when reading, but checks if the data has changed since it was read (for example, using a version or timestamp). If the data has changed, the transaction is rolled back and retried. This increases concurrency but requires conflict handling.
Example:
- Pessimistic:
SELECT ... FOR UPDATE— locks rows immediately. - Optimistic: storing a record version and checking it before updating.
The choice depends on the workload characteristics and the likelihood of conflicts.