Ad hoc query stubs in plan cache

This metric measures the total number of one-time use ad hoc queries in the plan cache that have been stored in the form of a stub, not as a full execution plan. It will only report values if the instance-level “optimize for ad hoc workloads” option is turned on. If this option if turned off (the default value) it will only return a zero.

A high value indicates that the “optimize for ad hoc workloads” is working effectively. A low value indicates that having “optimize for ad hoc workloads” turned on for the instance may not be a good idea, as a low number indicates that your instance is not suffering from plan cache bloat, and in addition, it may be causing ad hoc queries to be recompiling more often than they need to be, which can hinder SQL Server performance.Like many SQL Server metrics, there is no perfect answer, and it is best to gather baseline data over time to see what is happening in your server. Generally speaking, if this value is less than 250, then the “optimize for ad hoc workloads” may not be particularly effective. But of course, this depends on your server.

One way to help you determine if “optimize for ad hoc workloads” should be on or off for a particular instance is to test. For example, if you turn off “optimize for ad hoc workloads”, and then watch the values of the custom metrics Ad hoc queries running once and Memory used by ad hoc queries running once, and these values grow substantially (for example, over 10,000 for the first metric and over 350 MB for the second metric), then you probably will want to turn “optimize for ad hoc workloads” back on. On the other hand, if the values of the above two metrics are below the recommended values, then you may want to leave “optimize for ad hoc workloads” turned off.


		
			
			
Transact-SQL
			
			SELECT SUM(CASE WHEN usecounts = 1
                THEN 1
                ELSE 0
           END) AS [Adhoc Plans Use Count of 1]
  FROM sys.dm_exec_cached_plans
  WHERE objtype = 'Adhoc'
    AND cacheobjtype = 'Compiled Plan Stub'
  GROUP BY objtype;
			
				
					
				
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						SELECT SUM(CASE WHEN usecounts = 1
                THEN 1
                ELSE 0
           END) AS [Adhoc Plans Use Count of 1]
  FROM sys.dm_exec_cached_plans
  WHERE objtype = 'Adhoc'
    AND cacheobjtype = 'Compiled Plan Stub'
  GROUP BY objtype;

Select all

master

60

Leave the Use a calculated rate of change between collections check box unchecked

Enabled

Ad hoc query stubs in plan cache

This alert is raised when the total number of one-time use ad hoc queries in the plan cache that have been stored in the form of a stub (not as a full execution plan) exceed the specified threshold. It will only report values if the instance-level “optimize for ad hoc workloads” option is turned on. If this option if turned off (the default value) it will only return a zero.

A high value indicates that the “optimize for ad hoc workloads” is working effectively. A low value indicates that having “optimize for ad hoc workloads” turned on for the instance may not be a good idea, as a low number indicates that your instance is not suffering from plan cache bloat, and in addition, it may be causing ad hoc queries to be recompiling more often than they need to be, which can hinder SQL Server performance.Like many SQL Server metrics, there is no perfect answer, and it is best to gather baseline data over time to see what is happening in your server. Generally speaking, if this value is less than 250, then the “optimize for ad hoc workloads” may not be particularly effective. But of course, this depends on your server.

One way to help you determine if “optimize for ad hoc workloads” should be on or off for a particular instance is to test. For example, if you turn off “optimize for ad hoc workloads”, and then watch the values of the custom metrics Ad hoc queries running once and Memory used by ad hoc queries running once, and these values grow substantially (for example, over 10,000 for the first metric and over 350 MB for the second metric), then you probably will want to turn “optimize for ad hoc workloads” back on. On the other hand, if the values of the above two metrics are below the recommended values, then you may want to leave “optimize for ad hoc workloads” turned off.

Below the defined threshholds

High:	50
Medium:	150
Low:	250

Note: These thresholds are intended as guideline values. If they seem too high or too low for your environment, replace them with values more suited to your server performance.

10 collections

Enabled

Ad hoc query stubs in plan cache

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