HADR_TIMER_TASK

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Description:

This wait type is when a thread is waiting for access to the list of availability group timers, and also to track the timer waits themselves.

(Books Online description: “Waiting to get the lock on the timer task object and is also used for the actual waits between times that work is being performed. For example, for a task that runs every 10 seconds, after one execution, AlwaysOn Availability Groups waits about 10 seconds to reschedule the task, and the wait is included here.”)

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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 863 in 2012 and 882 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 a timer to expire
2. Waiting for the lock on the timer object to add a new timer
3. Waiting for the lock on the timer object to add a new timer

And other similar call stacks.

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

1. SOS_Task::PostWait+90
   EventInternal<SuspendQueueSLock>::Wait+1f9
   HadrTimerTask::RunTimerRoutine+505
   HadrTimerTask::TimerRoutine+1e
   HadrWorkItem::Execute+151
   HadrWorkRoutine+1c5
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8
2. SOS_Task::PostWait+90
   EventInternal<SuspendQueueSLock>::Wait+2c6
   SOS_RWLock::GetLongWait+10b
   HadrTimerTask::AddWorkItem+17e
   HadrWorkItem::SetTimeout+a3
   HadrWorkResource::EnqueueWork+19e
   DbMgrPartner::QueueBuildMsgAndSendTask+148
   DbMgrPartner::StartScans+403
   HadrWorkItem::Execute+151
   HadrWorkRoutine+1c5
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8
3. SOS_Task::PostWait+90
   EventInternal<SuspendQueueSLock>::Wait+2c6
   SOS_RWLock::GetLongWait+10b
   HadrTimerTask::AddWorkItem+17e
   HadrWorkItem::SetTimeout+a3
   HadrWorkResource::EnqueueWork+19e
   CHadrTransportReplica::QueueVersionedTask+b9
   CHadrTransportReplica::DetectTimeout+19d
   CHadrTransportReplica::DetectTimeoutTask+ae
   HadrWorkItem::Execute+151
   HadrWorkRoutine+1c5
   SOS_Task::Param::Execute+21e
   SOS_Scheduler::RunTask+a8