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Description:
This latch class is when a thread is waiting for access to the per-backup pool of worker threads. The name of this latch class and (the Books Online description) is quite misleading, as all backups can use multiple threads.
(Books Online description: “Used to synchronize backup tape pools.”)
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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_TAPEPOOL map_value in sys.dm_xe_map_values.
The map_key value in sys.dm_xe_map_values is 26 in 2008 and 2008 R2, and 21 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):
- Creating the pool of worker threads
Abbreviated call stacks (list number matches known occurrences list):
- XeSqlPkg::latch_suspend_end::Publish+138
LatchBase::Suspend+16b8
LatchBase::AcquireInternal+415
BackupWorkerPool::StartPool+67
BackupOperation::ProcessMediaHeaders+20e
BackupOperation::InitiateStartOfBackup+1ea
BackupEntry::BackupDatabase+304
CStmtDumpDb::XretExecute+ef
CMsqlExecContext::ExecuteStmts<1,1>+427
CMsqlExecContext::FExecute+a33
CSQLSource::Execute+86c