Warning: Failure to calculate super-latch promotion threshold

10 July,2014 by Jack Vamvas

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: Jack Vamvas (http://www.sqlserver-dba.com)


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