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Description:
This wait type is when a thread is calling out to Windows to initialize the SQM error reporting functionality.
(Books Online description: N/A)
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Added in SQL Server version:
2008
Removed in SQL Server version:
2017
Extended Events wait_type value:
Maps to the PREEMPTIVE_SQMLAUNCH map_value in sys.dm_xe_map_values (thanks to Jonathan’s post here).
The map_key value in sys.dm_xe_map_values is 520 in 2008 and 2008 R2, 568 in 2012, and 584 in 2014 RTM. After 2014 RTM, you must check the DMV to get the latest value as some map_key values have changed in later builds.
Other information:
I have not seen this wait type be a noticeable contention point.
Note that when a thread calls out to Windows, the thread changes from non-preemptive (SQL Server controls the thread) to preemptive (Windows controls the thread) mode. The thread’s state will be listed as RUNNING, as SQL Server doesn’t know what Windows is doing with the thread.
Known occurrences in SQL Server (list number matches call stack list):
- Initializing the SQM system
Abbreviated call stacks (list number matches known occurrences list):
- SOS_Task::PopWait+b1
SOS_ExternalAutoWait::~SOS_ExternalAutoWait+7c
CTaskSqlSqmLauncher::ProcessTskPkt+2be
TaskReqPktTimer::ExecuteTask+63
OnDemandTaskContext::ProcessTskPkt+3e2
SystemTaskEntryPoint+426
OnDemandTaskContext::FuncEntryPoint+25
OnDemandTaskContext::InitEntryPoint+8c
SOS_Task::Param::Execute+21e
SOS_Scheduler::RunTask+ab