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SOS_DISPATCHER_MUTEX

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Description:

This wait type is when a thread is waiting for access to a critical section of code inside the generic code that manages dispatching threads from a thread pool.

(Books Online description: “Occurs during internal synchronization of the dispatcher pool. This includes when the pool is being adjusted.”)

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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 339 in 2008 and 2008 R2, 386 in 2012, and 402 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.

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

  1. Waiting for the mutex for thread dispatching (in this case, for the thread pool created for backup and restore operations)

And other similar call stacks.

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

  1. SOS_Task::PostWait+9e
    EventInternal<SuspendQueueSLock>::Wait+1fb
    TAutoMutex<SOS_Mutex,1>::GetAccess+103
    SOS_DispatcherPool<BackupWorkItem,BackupWorkItem,SOS_DispatcherQueue<BackupWorkItem,0,BackupWorkItem>,BackupDispatcherPoolConfig,BackupWorkerContext * __ptr64>::DispatcherTerminated+46
    Dispatcher<BackupWorkItem,BackupWorkItem,SOS_DispatcherQueue<BackupWorkItem,0,BackupWorkItem>,BackupDispatcherPoolConfig,BackupWorkerContext * __ptr64>::Run+251
    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+a8