Backend

How to handle webhook idempotency and retries in production with durable receipts, atomic deduplication, fast acknowledgements, and replay-safe workers.

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

How to prevent race conditions in backend systems by naming the invariant, enforcing it at durable boundaries, and testing overlapping requests and retries.

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

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