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HADR_AG_MUTEX

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Description:

This wait type is when a thread is waiting for access to a critical section of code (one which only one thread can be executing) as part of examining or changing the configuration of an availability group.

(Books Online description: “Occurs when an AlwaysOn DDL statement or Windows Server Failover Clustering command is waiting for exclusive read/write access to the configuration of an availability group.”)

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Added in SQL Server version:

2012

Removed in SQL Server version:

N/A

Extended Events wait_type value:

The map_key value in sys.dm_xe_map_values is 777 in 2012 and 795 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 access to the AG configuration (in this case, to read the list of listeners during synchronization)

And other similar call stacks.

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

  1. SOS_Task::PostWait+90
    EventInternal<SuspendQueueSLock>::Wait+1f9
    SOS_RecursiveMutex::Wait+78
    AutoRecursiveAgMutexHolder::AutoRecursiveAgMutexHolder+e9
    CHadrArProxy::GetListenerEnumerator+58
    CHadrArController::GetAgListenerEnumerator+2a
    HadrAvailabilityGroupListenerEnumAll::GetNext+c1
    HadrAvailabilityGroupListenerEnumAll::GetFirst+36
    HadronTdsListenerSynchronizer::Synchronize+5c
    HadronTdsListenerSynchronizer::IdempotentWork+3c
    AsyncIdempotencyWithRedundancyReduction<HadronTdsListenerSynchronizer,4195159,10>::IdempotentWorkLoop+2ba
    SOS_Task::Param::Execute+21e
    SOS_Scheduler::RunTask+a8