(Republishing, or using this info in a commercial product/website, is prohibited without permission. All other uses are permitted. If in doubt, please ask.)

DISPATCHER_QUEUE_SEMAPHORE

(Back to main page…)

Description:

This wait type is when a thread from a special dispatcher pool is waiting for work to do. Parts of SQL Server that I know use their own thread pool is the backup subsystem and the In-Memory OLTP system in the Storage Engine.

(Books Online description: “Occurs when a thread from the dispatcher pool is waiting for more work to process. The wait time for this wait type is expected to increase when the dispatcher is idle.”)

Questions/comments on this wait type? Click here to send Paul an email, especially if you have any information to add to this topic.

Added in SQL Server version:

2008

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 330 in 2008 and 2008 R2, 377 in 2012, and 393 in 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.

This wait type is one that I usually filter out as a benign wait when doing wait statistics analysis.

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

  1. Waiting for some work to do (in this case, while executing a BACKUP operation)

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

  1. SOS_Task::PostWait+9e
    SOS_Semaphore::Wait+1a2
    SOS_DispatcherQueue<BackupWorkItem,0,BackupWorkItem>::Dequeue+63
    Dispatcher<BackupWorkItem,BackupWorkItem,SOS_DispatcherQueue<BackupWorkItem,0,BackupWorkItem>,BackupDispatcherPoolConfig,BackupWorkerContext * __ptr64>::Run+9c
    BackupWorkerPool::DispatcherEntryPoint+36
    SOS_DispatcherPool<BackupWorkItem,BackupWorkItem,SOS_DispatcherQueue<BackupWorkItem,0,BackupWorkItem>,BackupDispatcherPoolConfig,BackupWorkerContext * __ptr64>::RunDispatcher+1c
    SOS_Task::Param::Execute+21e
    SOS_Scheduler::RunTask+ab