DISPATCHER_QUEUE_SEMAPHORE is recorded by threads in a dispatcher pool, a special-purpose thread pool some subsystems maintain separately from the main worker pool, while they wait for work to arrive. Known users of dispatcher pools include the backup subsystem, In-Memory OLTP’s storage engine components, and Extended Events dispatching.
Idle pool threads waiting at the queue is the design working; the wait time is their time on the bench.
Is It a Problem?
No; Books Online notes explicitly that the wait time is expected to increase when the dispatcher is idle, which is most of the time on most systems. It is filtered as benign, and its totals scale with pool sizes and uptime rather than with any workload symptom.
The features it serves have their own real metrics when you need them: backup durations and throughput, In-Memory OLTP checkpoint file health, XE session buffer stats. The bench time of their thread pools contributes nothing to those investigations.
Common Causes
- Dispatcher pools existing (backup subsystem, In-Memory OLTP, XE) with spare capacity.
- Quiet periods leaving pool threads idle.
What To Do
- Filter it out of wait analysis; our
Get-WaitStatisticsscript excludes it by default. - Investigate the owning feature directly when it misbehaves; this wait will not tell you which feature anyway.
- Do not read idle pool threads as wasted resources; the pools are deliberately provisioned ahead of demand.
How To See It
Rank waits with Get-WaitStatistics, where it is filtered as background noise.
Part of the SQL Server Wait Types Library.
Related deep dive: SOS_SCHEDULER_YIELD Wait Type.
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