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This wait type is when a thread is waiting for an assembly to load into memory.
(Books Online description: “Occurs during exclusive access to assembly loading.”)
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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 298 in 2008 and 2008 R2, 341 in 2012, and 357 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):
Abbreviated call stacks (list number matches known occurrences list):