BACKUP_OPERATION

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Description:

This latch class is when a thread is waiting for access to the data structure within a BackupOperation class, which manages a single backup. The data structure holds information about the backup media, the database being backed up, the backup options, timing and LSN information, and so on.

(Books Online description: “Used for internal data structure synchronization within a backup operation, such as database, log, or file backup.”)

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Added in SQL Server version:

pre-2005/2005

Removed in SQL Server version:

N/A

Extended Events latch_class value:

Maps to the BACKUP_OPERATION_LOCK map_value in sys.dm_xe_map_values.

The map_key value in sys.dm_xe_map_values is 31 in 2008 and 2008 R2, and 26 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. Write the information about the database to the backup
2. Unknown, but from the call stack, possibly information about the backup file itself? (e.g. size?)
3. Unknown, but from the call stack, possibly writing out the start of a set of DBLKs (part of the Microsoft Tape Format, which is how backups are stored)
4. Unknown, but from the call stack, possibly writing out information about the media set that the backup is being written to
5. Unknown, but from the call stack, possibly looking up how big this backup stream should be

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

1. XeSqlPkg::latch_suspend_end::Publish+138
   LatchBase::Suspend+16cb
   SQL_FILE_INFO::Write+1c2
   BackupMedium::WriteDescription+1a0
   BackupMedium::WriteLeadingMetadata+145
   BackupStream::ThreadMainRoutine+1da
   BackupThread::ThreadBase+51
   SubprocEntrypoint+a59
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8
2. XeSqlPkg::latch_suspend_end::Publish+138
   LatchBase::Suspend+16cb
   SQL_FILE_INFO::Write+1c2
   BackupMedium::WriteDescription+130
   BackupMedium::WriteTrailingMetadata+138
   BackupStream::ThreadMainRoutine+1e7
   BackupThread::ThreadBase+51
   SubprocEntrypoint+a59
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8
3. XeSqlPkg::latch_suspend_end::Publish+138
   LatchBase::Suspend+16cb
   BackupOperation::SetOperatorName+13f
   BackupMedium::WriteStartOfSet+145
   BackupStream::ThreadMainRoutine+1c4
   BackupThread::ThreadBase+51
   SubprocEntrypoint+a59
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8
4. XeSqlPkg::latch_suspend_end::Publish+138
   LatchBase::Suspend+16cb
   BackupOperation::RecordCatalogMedia+145
   BackupMedium::WriteMbc+ff
   BackupStream::ThreadMainRoutine+228
   BackupThread::ThreadBase+51
   SubprocEntrypoint+a59
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8
5. XeSqlPkg::latch_suspend_end::Publish+138
   LatchBase::Suspend+16cb
   BackupStreamSizer::GetAllocation+140
   BackupStream::DoFileBackup+152
   BackupStream::ThreadMainRoutine+123
   BackupThread::ThreadBase+51
   SubprocEntrypoint+a59
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8