MSSQL-TOPQUERY-001 · A single query dominates CPU

Severity	Confidence	Permission	Applies to
Medium	Hint	VIEW SERVER STATE	SQL Server 2017+, Azure SQL MI, RDS, Azure SQL Database

What it checks

sys.dm_exec_query_stats grouped by query_hash. Reported when the most expensive query uses at least 40% of the CPU recorded in the plan cache (dominant_pct) and the cache holds at least 60 s of CPU (min_total_cpu_s). The evidence lists the top 5 with share, executions, average CPU, duration and reads.

On Azure SQL Database the plan cache covers only the connected database.

Why it matters

Tuning a database is rarely tuning everything. When one query dominates, fixing it is the change with the highest return.

Next action

Get the plan for the top query (sys.dm_exec_query_plan, or Query Store if enabled), look for scans, missing indexes, implicit conversions and bad estimates. Also check whether it runs more often than the application needs.

Limitations

The plan cache is emptied on restart and under memory pressure; OPTION (RECOMPILE) queries may be missing. Without history you can't tell when the query started dominating.