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This wait type is when a thread in a parallel restore is waiting for access to an output result set. The result set is being shared by the parallel threads so there has to be synchronization around entering new rows into it.
(Books Online description: “Occurs when serializing output produced by RESTORE HEADERONLY, RESTORE FILELISTONLY, or RESTORE LABELONLY.”)
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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 130 in 2008 and 2008 R2, and 134 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.
Known occurrences in SQL Server (list number matches call stack list):
- Waiting for access to the parallel result set
Abbreviated call stacks (list number matches known occurrences list):