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SQL Server and Xeon Hyperthreading CPU

I just got a new present from my boss, and I didn’t even know it was coming. It is an IBM eServer xSeries 255. It has 6GB RAM, 4 XEON, 2GHz Hyperthreading CPUs, and over 160GB of disk space. What is really impressive are the CPUs. The hyperthreading feature makes the OS think that there are 8 CPUs. It will be interesting to see how this server works in a production mode. When I installed SQL Server on it, it installed so fast that I thought that I must have made a mistake. It was just that fast. Anyone in the forum tried this hypterthreading CPU yet and gotten any experience with how it works with SQL Server? ——————
Brad M. McGehee
I’ve seen a little boost when running with hyperthreading but no where near having 2x the physical procs. I believe you’ll need to buy 8-cpu licenses to run w/ hp on your box. The cost of the licensing doesn’t really out weight the performance improvement you’ll get. If you do run out of steam, go with 8 physical procs…
Actually you DO NOT need to buy 8 processor licenses of SQL. Microsoft made some additions to their licensing that covers the XEON HTT type processor that windows sees at 2 processors even though it is one physical processor. Microsoft says… Per Processor Licensing
For currently available Microsoft servers products licensed on a per processor basis (e.g., Microsoft SQL Serverâ„¢, Microsoft BizTalk Serverâ„¢, Microsoft Content Management Serverâ„¢, etc.), one processor license for each physical processor on the server is required. Therefore, customers only need to acquire one processor license for each physical HTT even though the software may count one HTT as two logical processors. See the full deal at: http://www.microsoft.com/licensing/downloads/hyper_threading.doc XEONs are cool!
Thanks for the info stevem123, I didn’t know this. ——————
Brad M. McGehee
I have a Dell with 4 hyperthreading Xeons too. Generally it has been pretty go but you need to remember that each logical cpu is 1/2 a real one. I have a query that was heavy on maths so we split it to run as two queries. We were very happy to see it double in speed. So we thought lets do it over all 8 processors. We were disapointed to see that improvements stopped after we had four jobs running. We came to the conclusion that pegging a logical cpu pegged the physical one so the benifit when maxing the system out were limited. It still runs like grease lightning compared to the box we had before. Tim…
Also note that when using queries that can be parallelized hyperthreading can actualy hurt performance. Set the processor control in server setting to use only the physical processers(by Processor ID) and affinity mask option. Set the number of processors to use for parallel queries to the number of physical processors.

I have worked on it, and even tested db server i.e sql server for performance testing on xeon 4 way 8 HT processor.
Though we encountered some problems when it comes to the kind of code u’r application uses. praveen