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This wait is when a thread is starting a distributed transaction.
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Added in SQL Server version:
Removed in SQL Server version:
Extended Events wait_type value:
The map_key value in sys.dm_xe_map_values is 438 in 2008 and 2008 R2, 486 in 2012, and 502 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.
I have not seen this wait type be a noticeable contention point.
Note that when a thread calls out to Windows, the thread changes from non-preemptive (SQL Server controls the thread) to preemptive (Windows controls the thread) mode. The thread’s state will be listed as RUNNING, as SQL Server doesn’t know what Windows is doing with the thread.
Known occurrences in SQL Server (list number matches call stack list):
- Starting a distributed transaction
Abbreviated call stacks (list number matches known occurrences list):