PREEMPTIVE_COM_RELEASEACCESSOR

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Description:

This wait type is when a thread is waiting for a call to the ReleaseAccessor 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 405 in 2008 and 2008 R2, 453 in 2012, and 469 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. Releasing a row accessor, in this case while performing a sort
2. Releasing a row accessor, in this case while performing a join

And other similar call stacks.

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

1. SOS_Task::PopWait+bc
   AutoSwitchPreemptive::~AutoSwitchPreemptive+9a
   CQScanRmtBaseNew::ReleaseAllAccessors+ae
   CQScanRmtBaseNew::CloseHelper+2a
   CQScanSortNew::BuildSortTable+26b
   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
   AutoSwitchPreemptive::~AutoSwitchPreemptive+9a
   CQScanRmtBaseNew::ReleaseAllAccessors+ae
   CQScanRmtBaseNew::CloseHelper+2a
   CQScanNew::Close+20
   CQScanHash::ConsumeBuild+3e2
   CQScanHash::Open+7f
   CQScanUpdateNew::Open+13c
   CQueryScan::StartupQuery+1e0
   CXStmtQuery::SetupQueryScanAndExpression+19f
   CXStmtQuery::InitForExecute+1f
   CXStmtQuery::ErsqExecuteQuery+2fb
   CXStmtDML::XretDMLExecute+2eb
   CXStmtDML::XretExecute+99
   CMsqlExecContext::ExecuteStmts<1,1>+352
   CMsqlExecContext::FExecute+878
   CSQLSource::Execute+7d3