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BACKUP

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Description:

This wait type is when a backup thread is waiting for synchronization with other backup threads.

(Books Online description: “Occurs when a task is blocked as part of backup processing.”)

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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 133 in 2008 and 2008 R2, and 137 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.

Known occurrences in SQL Server (list number matches call stack list):

  1. Acquire an internal backup lock (in this case, during a restore)
  2. Waiting for the zeroing of a restored log file to complete
  3. Waiting for some log to process (in this case, during an fn_dump_dblog operation)

And other similar call stacks.

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

  1. SOS_Task::PostWait+90
    EventInternal<SuspendQueueSLock>::Wait+1f9
    AutoBackupLongLock::Get+41
    BackupMedium::Restore+a60
    BackupStream::DoRestore+6e
    BackupStream::ThreadMainRoutine+207
    BackupThread::ThreadBase+51
    SubprocEntrypoint+a59
    SOS_Task::Param::Execute+21e
    SOS_Scheduler::RunTask+a8
  2. SOS_Task::PostWait+90
    EventInternal<SuspendQueueSLock>::Wait+1f9
    BackupOperation::FinishLogZeroing+5b
    BackupMedium::Restore+544
    BackupStream::DoRestore+6e
    BackupStream::ThreadMainRoutine+207
    BackupThread::ThreadBase+51
    SubprocEntrypoint+a59
    SOS_Task::Param::Execute+21e
    SOS_Scheduler::RunTask+a8
  3. SOS_Task::PostWait+90
    EventInternal<SuspendQueueSLock>::Wait+1f9
    BackupLogRedoMachine::WaitForPacket+131
    BackupLogRedoMachine::SelectStreamForRedo+10f
    BackupLogRedoMachine::DriveRedo+68
    BackupOperation::RestoreDataFromMedia+195
    BackupOperation::VerifyRemainingBackupSet+38
    BackupOperation::VerifyBackupSet+12d
    BackupEntry::DumpLogVerify+7f
    SubprocEntrypoint+a59
    SOS_Task::Param::Execute+21e
    SOS_Scheduler::RunTask+a8