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Description:
This wait type is when a thread is waiting for various database mirroring configuration and state change operations to complete, including log flushes. It is typical to see many of these and it is a benign wait that you can usually filter out.
(Books Online description: “Occurs when a task is waiting for log records to be flushed to disk. This wait state is expected to be held for long periods of time.”)
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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 118 in 2008 and 2008 R2, and 122 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 wait type be a noticeable contention point but I have heard anecdotal evidence that if it’s one of the most prevalent waits, you could try increasing the performance of the I/O subsystem where the mirror database log file resides.
This wait type is one that I usually filter out as a benign wait when doing wait statistics analysis, but if you have a mirroring performance issues you could include it and see if doing the above helps overall performance.
Known occurrences in SQL Server (list number matches call stack list):
- Waiting for a database mirroring state change to finish (in this case, as part of running an ALTER DATABASE operation)
And other similar call stacks.
Abbreviated call stacks (list number matches known occurrences list):
- SOS_Task::PostWait+9e
EventInternal<SuspendQueueSLock>::Wait+1fb
LsMgr::WaitOnCommandDone+74
LsMgr::Configure+53b
DBMirroring::Configure+315
CStmtAlterDB::XretExecute+d7b
CMsqlExecContext::ExecuteStmts<1,1>+427
CMsqlExecContext::FExecute+a43
CSQLSource::Execute+86c
process_request+a57
process_commands+4a3
SOS_Task::Param::Execute+21e
SOS_Scheduler::RunTask+ab