How to Find the Top Most Expensive Cached Queries: sys.dm_exec_query_stats

Introduction

sys.dm_exec_query_stats DMV (Dynamic Management View) is described in BOL as follows: http://msdn.microsoft.com/en-us/library/ms189741.aspx

It returns aggregate performance statistics for cached query plans. The view contains one row per query statement within the cached plan, and the lifetime of the rows are tied to the plan itself. When a plan is removed from the cache, the corresponding rows are eliminated from this view. An initial query of sys.dm_exec_query_stats might produce inaccurate results if there is a workload currently executing on the server. More accurate results may be determined by rerunning the query.

sys.dm_exec_query_stats provides a wealth of performance statistics for cached query plans. It’s a very useful DMV to get cached query details for performance and server load analysis.

Query 1: Top 10 Total CPU Consuming Queries

SELECT TOP 10
QT.TEXT AS STATEMENT_TEXT,
QP.QUERY_PLAN,
QS.TOTAL_WORKER_TIME AS CPU_TIME
FROM SYS.DM_EXEC_QUERY_STATS QS
CROSS APPLY SYS.DM_EXEC_SQL_TEXT (QS.SQL_HANDLE) AS QT
CROSS APPLY SYS.DM_EXEC_QUERY_PLAN (QS.PLAN_HANDLE) AS QP
ORDER BY TOTAL_WORKER_TIME DESC

Query 2: Top 10 Average CPU Consuming Queries

SELECT TOP 10
TOTAL_WORKER_TIME ,
EXECUTION_COUNT ,
TOTAL_WORKER_TIME / EXECUTION_COUNT AS [AVG CPU TIME] ,
QT.TEXT AS QUERYTEXT
FROM SYS.DM_EXEC_QUERY_STATS QS
CROSS APPLY SYS.DM_EXEC_SQL_TEXT(QS.PLAN_HANDLE) AS QT
ORDER BY QS.TOTAL_WORKER_TIME DESC ;

Query 3: Top 10 I/O Intensive Queries

SELECT TOP 10
TOTAL_LOGICAL_READS,
TOTAL_LOGICAL_WRITES,
EXECUTION_COUNT,
TOTAL_LOGICAL_READS+TOTAL_LOGICAL_WRITES AS [IO_TOTAL],
QT.TEXT AS QUERY_TEXT,
DB_NAME(QT.DBID) AS DATABASE_NAME,
QT.OBJECTID AS OBJECT_ID
FROM SYS.DM_EXEC_QUERY_STATS QS
CROSS APPLY SYS.DM_EXEC_SQL_TEXT(SQL_HANDLE) QT
WHERE TOTAL_LOGICAL_READS+TOTAL_LOGICAL_WRITES > 0
ORDER BY [IO_TOTAL] DESC 

Query 4: Execution Count of Each Query

SELECT QS.EXECUTION_COUNT,
QT.TEXT AS QUERY_TEXT,
QT.DBID,
DBNAME= DB_NAME (QT.DBID),
QT.OBJECTID,
QS.TOTAL_ROWS,
QS.LAST_ROWS,
QS.MIN_ROWS,
QS.MAX_ROWS
FROM SYS.DM_EXEC_QUERY_STATS AS QS
CROSS APPLY SYS.DM_EXEC_SQL_TEXT(QS.SQL_HANDLE) AS QT
ORDER BY QS.EXECUTION_COUNT DESC

Remarks

1. Statistics in the view are updated when a query is completed.
2. User required VIEW SERVER STATE permission on the server.

Reference

• Rohit Garg (http://mssqlfun.com/)