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DATABASE_MIRRORING_STREAM

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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.”)

Questions/comments on this latch class? Click here to send Paul an email, especially if you have any information to add to this topic.

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):

  1. Unknown, but from the call stack, my guess is that it’s building a list of received messages or portions of a message
  2. Receiving a log stream buffer on the mirror server

And many more similar call stacks.

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

  1. 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
  2. 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