PARALLEL_BACKUP_QUEUE is recorded when a thread in a parallel restore operation waits for access to a shared output result set. The commands that read backup metadata, RESTORE HEADERONLY, RESTORE FILELISTONLY, RESTORE LABELONLY, build their output rows from parallel workers, and those workers must take turns inserting into the shared rowset.
It is queueing around a result set, not around the actual data movement of a restore.
Is It a Problem?
No; it has not been a contention point, and its scale is bounded by how often you interrogate backup files. Environments where monitoring tools or restore-verification jobs run RESTORE HEADERONLY against many backups on a schedule will accumulate more of it, and even then the amounts stay trivial.
If metadata restores themselves feel slow, the time is nearly always reading the backup media (especially tape, cloud URLs, or deduplicating appliances), not this rowset synchronisation.
Common Causes
RESTORE HEADERONLY/FILELISTONLY/LABELONLYcommands, ad hoc or scheduled.- Backup verification tooling sweeping backup files regularly.
- Slow backup media stretching the overall command while workers coordinate.
What To Do
- Nothing for the wait itself.
- If backup interrogation jobs are slow, measure read throughput from the backup target; that is where the time goes.
- Keep verification jobs off peak windows if they share storage with production backups.
How To See It
Rank it against everything else with Get-WaitStatistics; expect only traces, correlated with restore-metadata activity.
Part of the SQL Server Wait Types Library.
Related deep dive: BACKUPIO and BACKUPBUFFER Wait Types.
Leave a Reply