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This wait type is just as described in Books Online. If nothing is happening on the mirrored database, these waits be be long.
(Books Online description: “Indicates that the database mirroring worker task is waiting for more work.”)
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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 141 in 2008 and 2008 R2, and 145 in 2012 and 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.
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):
- Waiting for some database mirroring work to do
Abbreviated call stacks (list number matches known occurrences list):