June 30, 2005 at 10:34 am
Here is yet another quandry:
I have a Windows 2003 server running SQL 2000 Enterprise with four processors. When I check the properties of my database and click on the processors, I see a total of 8 processors that are registering.
What is the deal? Does this have something to do with the way SQL is reading the threading?
June 30, 2005 at 11:03 am
Let me guess... you are using P4 or P4 Xeon chips. This is the hyperthreading, but even though SQL "sees" 8 CPU's you only need to license 4.
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If most people are not willing to see the difficulty, this is mainly because, consciously or unconsciously, they assume that it will be they who will settle these questions for the others, and because they are convinced of their own capacity to do this. -Friedrich August von Hayek
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June 30, 2005 at 11:49 am
Correct. This is hyperthreading. The SQL Server Central.com boxes are 2 way, but show up as 4. There's been some debate as to whether or not hyperthreading is bad for SQL Server. I might turn it off in the bios and test to see if things run better.
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June 30, 2005 at 11:59 am
Yeah, I wondered about HT's potential negative effects. The main one being additional parallelism without the benefit of actually having seperate CPU's. I have run our servers both ways and our tests seemed to indicate that HT is pretty much a wash...
/*****************
If most people are not willing to see the difficulty, this is mainly because, consciously or unconsciously, they assume that it will be they who will settle these questions for the others, and because they are convinced of their own capacity to do this. -Friedrich August von Hayek
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June 30, 2005 at 12:11 pm
This is what I thought after the server admin told me that this server had hyper-threading, I just didn't know exactly how SQL handled it.
If there are no known side-effects of HT on SQL I will keep things as they are for now.
Thanks!
July 1, 2005 at 7:53 am
To my knowledge there are no known issues outstanding with HT on P4 processors relating to SQL. But you really won't notice a bennifit until the CPU hits above 80% and you would have to have known what it was like without HT on for the same CPU utilization. Benchmarks don't show a significant jump even then thou. But more concurrent threads are good in handling loads overall. I am wanting to pick up the P4 Extreme with dual cores and HT which looks like 4 processors to SQL but Miscrosoft has stated they only license based on physical processors and not logical (so 1 processor license instead of 4). The dual-cores will be well worth the purchase especially for machines which are considering moving to 2 processors.
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