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PREEMPTIVE_DTC_ENLIST

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Description:

This wait is when a thread is calling into DTC to register a new DTC resource manager.

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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 440 in 2008 and 2008 R2, 488 in 2012, and 504 in 2014.

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):

  1. Creating a new DTC resource manager

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

  1. SOS_Task::PopWait+b1
    AutoSwitchPreemptive::~AutoSwitchPreemptive+95
    DtcXactRMOnly::Init+c03
    XactMgr::CreateNewDTCRM+194
    FullXactImp::MakeDistributed+b8
    CXStmtXactBegin::XretExecute+296
    CMsqlExecContext::ExecuteStmts<1,1>+427
    CMsqlExecContext::FExecute+a43
    CSQLSource::Execute+86c