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This wait type is when a thread is waiting for an operation to do with the log pool. This is an in-memory cache of recently flushed log blocks, to help avoid log readers having to do physical reads of the log file (e.g. for sending log blocks to asynchronous availability group replicas).
(Books Online description: N/A)
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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 769 in 2012 and 787 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):
- Changing the log pool cache size for a database (in this case, while performing a checkpoint as a database is going offline)
- Changing the log pool cache size for a database (in this case, while performing a checkpoint for a database in the simple recovery mode, where the checkpoint has allowed some VLFs to be made inactive and they no longer need to take up space in the log pool)
And other similar call stacks.
Abbreviated call stacks (list number matches known occurrences list):