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Description:
This wait type is when a thread is waiting for the TDS communication protocol to initialize for the Dedicated Admin Connection (DAC) listener. The DAC is a separate connection that can be used to connect to an unresponsive server to troubleshoot and kill connections that are causing SQL Server to be unresponsive. See Books Online here for more details.
(Books Online description: “Occurs while the dedicated administrator connection is initializing.”)
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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 297 in 2008 and 2008 R2, 340 in 2012, and 356 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):
- Initializing the TDS protocol for the DAC listener while SQL Server is starting
Abbreviated call stacks (list number matches known occurrences list):
- SOS_Task::PostWait+9e
EventInternal<SuspendQueueSLock>::Wait+2aa
SOS_Task::WaitForDone+a0
InitializeTDS+2d1
FRunCommunicationsManager+4e
CommunicationsManager+3c6
SOS_Task::Param::Execute+21e
SOS_Scheduler::RunTask+ab