Backend

How to compare SKIP LOCKED, plain FOR UPDATE, and advisory lock job claims in PostgreSQL with a runnable pgbench harness and a claim-strategy decision table.

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

How database connection pool exhaustion happens under load, how to tell pool wait from slow SQL, and how to size pools across instances safely.

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.