Diagnoses and optimizes SQL Server database performance. Use when diagnosing slow T-SQL queries, tuning indexes, reading execution plans, fixing parameter sniffing, optimizing batch operations, reducing transaction log bloat, troubleshooting locking and blocking, configuring tempdb, or when a query that used to be fast is now slow. Also use when writing high-throughput INSERT/UPDATE/DELETE operations, implementing minimal logging, designing covering indexes, or analyzing wait statistics.