Databases

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.

A practical rollout plan for safe database migrations using expand-and-contract, phased constraints, resumable backfills, rollback planning, and production monitoring.

A production workflow for finding slow SQL queries, reading EXPLAIN plans, choosing fixes, and proving the endpoint improved.

How to detect and fix the N+1 query problem in ORMs with query counts, SQL traces, eager loading, batched IN queries, request-scoped loaders, and production rollout checks.