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The Books Online entry for this is really confused. This wait type is when the coordinator thread of an fn_dump_dblog operation is waiting for sub-threads to complete an operation. This is normal to see when running fn_dump_dblog to view log records in a backup.
(Books Online description: “Occurs when a main task is waiting for a subtask to generate data. Ordinarily, this state does not occur. A long wait indicates an unexpected blockage. The subtask should be investigated.”)
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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 147 in 2008 and 2008 R2, and 151 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 a dump log sub-thread to finish (in this case, while exiting the log backup dumping operation)
And other similar call stacks.
Abbreviated call stacks (list number matches known occurrences list):