MSQL_DQ

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Description:

This wait type is exactly as described by the Books Online entry (although the second sentence should say ‘This is *also* used to detect…’).

(Books Online description: “Occurs when a task is waiting for a distributed query operation to finish. This is used to detect potential Multiple Active Result Set (MARS) application deadlocks. The wait ends when the distributed query call finishes.”)

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Added in SQL Server version:

Pre-2005/2005

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 201 in 2008 and 2008 R2, 208 in 2012, and 215 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:

If this wait type becomes prevalent on your server, identify the queries causing it, and do performance analysis on the portions of the query that run on the remote SQL Server or other OLE DB data provider. For more information, see the Books Online topic Optimizing Distributed Queries.

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

1. Waiting for a remote data provider to respond, in this case while retrieving a remote rowset as input into a local sort
2. Waiting for a remote data provider to respond, in this case while running the sp_testlinkedserver procedure
3. Waiting for a remote data provider to respond, in this case while retrieving remote statistics while compiling a query plan

And other similar call stacks.

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

1. SOS_Task::PopWait+bc
   COledbConnect::GetSession+715
   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
   COledbConnect::GetSession+715
   SpTestLinkedServer+241
   CSpecProc::ExecuteSpecial+25b
   CXProc::Execute+14e
   CSQLSource::Execute+90e
   CStmtExecProc::XretLocalExec+1e4
   CStmtExecProc::XretExecExecute+527
   CXStmtExecProc::XretExecute+27
   CMsqlExecContext::ExecuteStmts<1,1>+352
   CMsqlExecContext::FExecute+878
   CSQLSource::Execute+7d3
   process_request+3fa
   process_commands+38c
   SOS_Task::Param::Execute+292
   SOS_Scheduler::RunTask+a2
3. SOS_Task::PopWait+bc
   COledbConnect::GetSession+715
   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
   process_request+3fa
   process_commands+38c
   SOS_Task::Param::Execute+292
   SOS_Scheduler::RunTask+a2