An explanation of optimistic and pessimistic locking strategies used to manage concurrent data access. Optimistic locking works by reading a record along with a version number or timestamp, then checking that version before writing to detect conflicts — if the version has changed, the update is discarded and the data must be re-read. Pessimistic locking exclusively locks a resource so no other process can modify it until the lock is released. The post covers when to use each: optimistic locking suits low-conflict scenarios like wiki article editing and distributed systems, while pessimistic locking suits high-conflict database row updates. Key drawbacks of pessimistic locking include deadlocks and the need for persistent connections, while optimistic locking can suffer from high retry rates under heavy contention.