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(Books Online description: “Occurs during internal synchronization in metadata on table or index.”)
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Added in SQL Server version:
Removed in SQL Server version:
Extended Events wait_type value:
Maps to the MD_RELATION_CACHE map_value in sys.dm_xe_map_values (thanks to Jonathan’s post here).
The map_key value in sys.dm_xe_map_values is 653 in 2012 and 671 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.
Known occurrences in SQL Server (list number matches call stack list):
Abbreviated call stacks (list number matches known occurrences list):