BACKUPTHREAD

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Description:

This wait type is when a backup thread is waiting for other threads to finish operations during a backup or restore.

(Books Online description: “Occurs when a task is waiting for a backup task to finish. Wait times may be long, from several minutes to several hours. If the task that is being waited on is in an I/O process, this type does not indicate a problem.”)

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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 136 in 2008 and 2008 R2, and 140 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. Waiting for a thread to complete (in this case, during a BACKUP LOG operation)
2. Waiting for a thread to complete (in this case, during a BACKUP DATABASE operation)

And many more similar call stacks.

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

1. SOS_Task::PostWait+90
   EventInternal<SuspendQueueSLock>::Wait+1f9
   BackupThread::Start+26f
   BackupStream::Spawn+7f
   BackupOperation::CopyLogToArchive+ad
   BackupOperation::PerformLogCopySteps+50
   BackupEntry::BackupLog+318
   CStmtDumpXact::XretExecute+ef
   CMsqlExecContext::ExecuteStmts<1,1>+400
   CMsqlExecContext::FExecute+a33
   CSQLSource::Execute+866
   process_request+73c
   process_commands+51c
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8
2. SOS_Task::PostWait+90
   EventInternal<SuspendQueueSLock>::Wait+1f9
   BackupThread::Wait+c3
   BackupStreamList::WaitUntilDone+4d
   BackupOperation::WaitForMediaWriters+2f
   BackupOperation::BackupData+39b
   BackupEntry::BackupDatabase+2ca
   CStmtDumpDb::XretExecute+ef
   CMsqlExecContext::ExecuteStmts<1,1>+400
   CMsqlExecContext::FExecute+a33
   CSQLSource::Execute+866
   process_request+73c
   process_commands+51c
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8