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This wait type occurs when a thread is waiting for reads from an external (to SQL Server) sequential stream source to complete. An example would be selecting from an OPENQUERY to an Oracle server.
(Books Online description: “Internal use only.”)
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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 409 in 2008 and 2008 R2, 457 in 2012, and 473 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.
If this wait type becomes unexpectedly prevalent, identify which query is causing it (using sys.dm_os_waiting_tasks) and troubleshoot performance of the data source involved.
Known occurrences in SQL Server (list number matches call stack list):
Abbreviated call stacks (list number matches known occurrences list):