Reliability

How to handle webhook idempotency and retries in production with durable receipt records, atomic deduplication, fast acknowledgements, idempotent workers, and replay-safe side effects.

How to build a PostgreSQL job queue with FOR UPDATE SKIP LOCKED, including schema design, atomic claiming, indexes, retries, stuck-job recovery, cleanup, and production trade-offs.

How to prevent race conditions in backend systems by naming the invariant, moving correctness to durable boundaries, and testing overlapping requests, retries, and jobs.

How to choose between optimistic locking, guarded updates, and SELECT FOR UPDATE in SQL when concurrent requests can overwrite data, oversell inventory, or serialize hot rows.

A practical guide to SQL isolation levels, including Read Committed, Repeatable Read, Serializable, database-specific behavior, locking trade-offs, and production examples.