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PREEMPTIVE_COM_QUERYINTERFACE

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Description:

This wait type is when a thread is waiting for a call to the QueryInterface method of a COM object to complete.

(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 403 in 2008 and 2008 R2, 451 in 2012, and 467 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’ve heard of this wait being an issue when using linked servers and the provider’s driver is not properly installed. For example:

  • Install the Oracle driver but do not reboot as instructed (this is where the mistake was made)
  • Modify the OraOLEDB.Oracle Provider to Allow In Process and do not restart the SQL instance
  • Create a linked server using the Oracle driver
  • Query the linked server and the query hangs with a wait type of PREEMPTIVE_COM_QUERYINTERFACE

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. Querying the COM object for the TransactionJoin interface, in this case while performing a sort operation
  2. Querying the COM object for the TransactionJoin interface, in this case while retrieving remote statistics

And other similar call stacks.

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

  1. SOS_Task::PopWait+bc
    SOS_Task::AutoSwitchPreemptive::~AutoSwitchPreemptive+72
    COledbConnect::GetSession+701
    COledbRangeSchema::GetRowset+cb
    COledbRangeSchema::GetRowset+2e4
    CQScanRmtScanNew::OpenConnection+1c4
    CQScanRmtBaseNew::OpenHelper+76
    CQScanSortNew::BuildSortTable+56
    CQScanSortNew::OpenHelper+cc
    CQScanSortNew::Open+10
    CQueryScan::StartupQuery+1e0
    CXStmtQuery::SetupQueryScanAndExpression+19f
    CXStmtQuery::InitForExecute+1f
    CXStmtQuery::ErsqExecuteQuery+2fb
    CXStmtSelect::XretExecute+28a
    CMsqlExecContext::ExecuteStmts<1,1>+352
    CMsqlExecContext::FExecute+878
    CSQLSource::Execute+7d3
  2. SOS_Task::PopWait+bc
    SOS_Task::AutoSwitchPreemptive::~AutoSwitchPreemptive+72
    COledbConnect::GetSession+701
    COledbRangeRowset::GatherStats+d8
    CRelOp_Query::LoadRemoteStats+28e
    CRelOp_Query::FAlgebrizeQuery+521
    CProchdr::FNormQuery+3d
    CProchdr::FNormalizeStep+3ce
    CSQLSource::FCompile+c85
    CSQLSource::FCompWrapper+9e
    CSQLSource::Transform+49c
    CSQLSource::Execute+3cf