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Warning: Failure to calculate super-latch promotion threshold
10 July,2014 by Tom Collins
Question: Why is the warning message Failure to calculate super-latch promotion threshold appearing in the SQL Server Error Log files?
Answer: First some background information. If thousands of queries are accessing a lookup value table in the data cache it’s refered as a hot page. These hot pages can experience latch contention. A sustained high level of SH activity can be promoted to a sub-latch. (sub-latch is an interchangeable term with super-latch).
The sub-latch is a single-latch scaled into a latch array per logical CPU. The worker can access just the sub-latch assigned to the related scheduler. Acquiring the sub-latch is less resource intensive and is a scalable method for hot page access.
For an in-depth explanation and troubleshooting read Diagnosing and Resolving Latch Contention on SQL Server . This is an excellent document that covers most aspects of this advanced area.
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Author: Tom Collins (http://www.sqlserver-dba.com)
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