Backend

How to roll out database schema changes safely in production without breaking reads, writes, deployments, or mixed-version application traffic.

How to write API integration tests that verify real persistence, auth rules, contracts, idempotency, and failure handling across request boundaries.

A production workflow for finding slow SQL queries, reading query plans, choosing the right fix, and rolling out database changes safely.

How idempotency keys prevent duplicate API writes, repeated side effects, and race conditions when clients retry under uncertain network behavior.

How to evolve APIs without breaking clients through explicit compatibility rules, staged rollouts, and deprecation workflows that teams can enforce.