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Description:
This latch class is when a thread is waiting for access to the communication stream for a database mirroring session.
(Books Online description: “Internal use only.”)
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Added in SQL Server version:
pre-2005/2005
Removed in SQL Server version:
I have not seen this latch be a noticeable contention point.
See the LATCH_EX wait type for more information about latches in general and how to troubleshoot them.
Extended Events latch_class value:
Maps to the DB_MIRRORING_STREAM map_value in sys.dm_xe_map_values.
The map_key value in sys.dm_xe_map_values is 77 in 2008 and 2008 R2, and 71 in 2012 and 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 latch be a noticeable contention point.
See the LATCH_EX wait type for more information about latches in general and how to troubleshoot them.
Known occurrences in SQL Server (list number matches call stack list):
- Unknown, but from the call stack, my guess is that it’s building a list of received messages or portions of a message
- Receiving a log stream buffer on the mirror server
And many more similar call stacks.
Abbreviated call stacks (list number matches known occurrences list):
- XeSqlPkg::latch_suspend_end::Publish+138
LatchBase::Suspend+16b8
LatchBase::AcquireInternal+415
DbmStream::Append+5e
DbmConnection::ProcessReceiveMessage+1f9
LsStateMachineBase::PostEvent+1d7
LsStateMgr::ProcessEvents+113
DbmDatabaseStateMgr::MasterThreadRoutine+303
SOS_Task::Param::Execute+21e
SOS_Scheduler::RunTask+a8 - XeSqlPkg::latch_suspend_end::Publish+138
LatchBase::Suspend+16b8
LatchBase::AcquireInternal+415
DbmStream::Receive+6f
LsBuffer::Receive+40
LsMgr::ProcessLogStream+520
LsMgr::ProcessLogStreamResponse+6e
LsWorkRequest::Execute+47
LsWorker::ThreadRoutine+152
LsWorker::ThreadRoutine+1c7
SOS_Task::Param::Execute+21e
SOS_Scheduler::RunTask+a8