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This wait type is when a thread that is performing log redo on an availability group secondary replica is waiting to be signaled that there is more log to redo.
(Books Online description: N/A)
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Added in SQL Server version:
Removed in SQL Server version:
Extended Events wait_type value:
Maps to the REDO_SIGNAL 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 752 in 2012 and 770 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 and on an availability group with very low amounts of log being generated, I would expect to see high wait times for this wait.
This wait type is one that I usually filter out as a benign wait when doing wait statistics analysis.
Known occurrences in SQL Server (list number matches call stack list):
Abbreviated call stacks (list number matches known occurrences list):