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This wait type is when a thread is waiting for exclusive access to the data structure that contains the latest log-harden LSN in an availability group primary replica. This is required when there is a synchronous replica, so that threads waiting for HADR_SYNC_COMMIT (i.e. waiting for the log blocks containing their LOP_COMMIT_XACT log records) as part of the transaction commit mechanism can be signaled that their commits have completed if their commit LSN is less than or equal to the latest log-harden LSN.
(Books Online description: “Concurrency control wait when updating the log progress status of database replicas.”)
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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 787 in 2012 and 805 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 prevalent, you will also see many HADR_SYNC_COMMIT waits, as committing transactions are delayed in being signaled that their commits have completed.
There is an excellent blog post from 2018 by Product Support here that investigates a scenario where this wait happens because of a thread on the same scheduler going non-yielding (fixed in 2016 SP1 CU7).
Known occurrences in SQL Server (list number matches call stack list):
Abbreviated call stacks (list number matches known occurrences list):