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SQL 2005 and hyperthreading

Posted on 2007-10-10
Medium Priority
Last Modified: 2013-11-29
I have a new x64 2 node cluster 4 - dual core procs 32GB RAM setup by our engineers.  They enabled hyperthreading and the OS is now showing 16 procs.  I plan to install SQL 2005 Ent on this and I'm thinking hyperthreading may not be in our best interest.  I'm concerned with the extra overhead affecting performance.  Our database applications tend to be more I/O intensive than processor intensive.  I was looking for a 'Best Practices' doc saying to disable hyperthreading but I'm not able to find anything specific.


Question by:BradyDBA
LVL 27

Accepted Solution

ptjcb earned 500 total points
ID: 20050843
SQL Server and hyperthreading are not friends.


FROM http://www.sqlmag.com/Article/ArticleID/96850/sql_server_96850.html

I have it on good authority (SQL Server MVP Geoff Hiten, FYI) that hyperthreading is still misbehaving on SQL Server 2005. Evidently, hyperthreading looks like a multi-core system to SQL Server 2005 thus triggering some "soft NUMA" behavior. As Geoff says, "The real problem comes in the synchronization primitives that aren't hyperthreaded friendly (such as spinlock code). SQL 2000 had a bug that was fixed in build 910 that dealt with this issue. This bug was re-introduced in SQL 2005 when they changed the memory and scheduler to handle multi-core processors and NUMA architectures. So, in short, I would turn off HT on SQL 2005 host computers as the default. As always, your mileage may vary." Great advice,

Hyper-Threading does not benefit typical SQL Server workloads
Generally recommend disabling Hyper-Threading
Potentially overloads a single core with multiple concurrent scheduler tasks
Multiple threads can thrash the CPU cache

FROM http://blogs.digineer.com/blogs/larar/archive/2006/11/13/maximum-degree-of-parallelism-and-hyperthreading.aspx

Hyperthreading should not be enabled on a SQL Server server unless it has been proven to improve performance.

Author Comment

ID: 20051172
Many thanks.

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