Performance Tuning with SQL Server Dynamic Management Views

Chapter 3: Query Plan Metadata
SELECT COUNT(*)
FROM sys.dm_exec_cached_plans ;
Listing 3.7: Total number of cached plans.
More useful though, is to get a feel for the "distribution" of plan reuse on your system. To
do this, we can group on the usecounts column, and use the CASE expression to roll up
bands of usecounts as shown in Listing 3.8.
SELECT MAX(CASE WHEN usecounts BETWEEN 10 AND 100 THEN '10-100'
WHEN usecounts BETWEEN 101 AND 1000 THEN '101-1000'
WHEN usecounts BETWEEN 1001 AND 5000 THEN '1001-5000'
WHEN usecounts BETWEEN 5001 AND 10000 THEN '5001-10000'
ELSE CAST(usecounts AS VARCHAR(100))
END) AS usecounts ,
COUNT(*) AS countInstance
FROM sys.dm_exec_cached_plans
GROUP BY CASE WHEN usecounts BETWEEN 10 AND 100 THEN 50
WHEN usecounts BETWEEN 101 AND 1000 THEN 500
WHEN usecounts BETWEEN 1001 AND 5000 THEN 2500
WHEN usecounts BETWEEN 5001 AND 10000 THEN 7500
ELSE usecounts
END
ORDER BY CASE WHEN usecounts BETWEEN 10 AND 100 THEN 50
WHEN usecounts BETWEEN 101 AND 1000 THEN 500
WHEN usecounts BETWEEN 1001 AND 5000 THEN 2500
WHEN usecounts BETWEEN 5001 AND 10000 THEN 7500
ELSE usecounts
END DESC ;
Listing 3.8: An overview of plan reuse.
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