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This wait type is when a thread is waiting for exclusive access to the parent rowset of a parallel scan, for coordination between the various child threads.
(Books Online description: “Occurs during a parallel range scan.”)
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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 363 in 2008 and 2008 R2, 410 in 2012, and 426 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. If you do not want parallelism, see the CXPACKET wait for more information.
Known occurrences in SQL Server (list number matches call stack list):
- Setting up a new scan
- Setting the range for a scan (in this case, as part of a nested-loops join)
Abbreviated call stacks (list number matches known occurrences list):