Software-engineering

How to test database migrations in CI with production-shaped data, compatibility checks, backfill verification, schema drift detection, and rollback gates.

How to diagnose flaky integration tests in CI: shared state, timing assumptions, parallel worker conflicts, database cleanup gaps, and unstable dependencies.

How to plan database migration rollback in production with compatibility windows, forward fixes, backfill recovery, and clear stop points.

How API contract testing catches breaking request, response, and schema changes before release with OpenAPI diffs, consumer examples, and CI checks.

How trace sampling affects production debugging: head, parent-based, and tail sampling trade-offs, error traces, rare paths, and async work.