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ONDEMAND_TASK_QUEUE

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Description:

As stated below. One example of high-priority system task request is a DTC commit/abort.

(Books Online description: “Occurs while a background task waits for high priority system task requests. Long wait times indicate that there have been no high priority requests to process, and should not cause concern.”)

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Added in SQL Server version:

2008

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 126 in 2008 and 2008 R2, and 130 in 2012 and 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:

This wait type is one that I usually filter out as a benign wait when doing wait statistics analysis.

Known occurrences in SQL Server (list number matches call stack list):

  1. Ending the wait for this type by getting an available system thread

Abbreviated call stacks (list number matches known occurrences list):

  1. SOS_Task::PostWait+9e
    EventInternal<SuspendQueueSLock>::Wait+2ca
    ResQueueBase::Dequeue+1cf
    systemTaskThread+216
    SOS_Task::Param::Execute+21e
    SOS_Scheduler::RunTask+a8