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PREEMPTIVE_OS_LOADLIBRARY

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Description:

This wait type is when a thread is calling the Windows LoadLibrary function.

(Books Online description: N/A)

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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 470 in 2008 and 2008 R2, 518 in 2012, and 534 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):

  1. Loading a library (in this case, to get version information for a DLL that implements one or more XPs)

And other similar call stacks.

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

  1. SOS_Task::PopWait+b1
    SOS_ExternalAutoWait::~SOS_ExternalAutoWait+7c
    FReadVersion+39e
    FCallRpcDLL+18e
    CXProc::Execute+51f
    CSQLSource::Execute+9ae
    CStmtExecProc::XretLocalExec+25a
    CStmtExecProc::XretExecExecute+4e8
    CXStmtExecProc::XretExecute+38
    CXStmtInsertExec::XretDoExecute+462
    CXStmtInsertExec::XretExecute+46
    CMsqlExecContext::ExecuteStmts<1,1>+427
    CMsqlExecContext::FExecute+a43
    CSQLSource::Execute+86c
    process_request+a57
    process_commands+4a3
    SOS_Task::Param::Execute+21e
    SOS_Scheduler::RunTask+ab