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This wait type is when a background thread is running the sp_server_diagnostics procedure. This was added for SQL Server 2012 to aid with automatic detection of failures to allow automatic failover with availability groups. You can read more about it:
(Books Online description: N/A)
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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 735 in 2012 and 753 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.
Known occurrences in SQL Server (list number matches call stack list):
- Running the sp_server_diagnostics procedure
Abbreviated call stacks (list number matches known occurrences list):