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Hyperthread or not?


Hyperthread or not?

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Indianrock
Indianrock
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We're still on sql 2005 enterprise 64-bit with plans to upgrade to 2012 later this year. We have one main production database of about 2.5TB which gets a mix of OLTP and OLAP queries with read to write ratio of 3.6 -- about 3.6 reads for each write. Netapp filer for storage. Sql allocated 370GB of memory.
Hyper-threading is active on our Dell Poweredge M910s ( active/passive cluster) Short of testing on production, any input on the value of having hyper-threading on.? We're about to set a server-wide max degree of parallelism of 16 since we do see quite a few queries using up a lot of threads -- cxpacket waits.

4 physical processors with 8 cores=32 64 Logical cpus with hyperthreading

OS Name: Microsoft Windows Server 2008 R2 Enterprise
OS Version: 6.1.7601 Service Pack 1 Build 7601
OS Manufacturer: Microsoft Corporation
OS Configuration: Member Server
OS Build Type: Multiprocessor Free
System Manufacturer: Dell Inc.
System Model: PowerEdge M910
System Type: x64-based PC
Processor(s): 4 Processor(s) Installed.
[01]: Intel64 Family 6 Model 47 Stepping 2 GenuineIntel ~2128 Mhz
[02]: Intel64 Family 6 Model 47 Stepping 2 GenuineIntel ~2128 Mhz
[03]: Intel64 Family 6 Model 47 Stepping 2 GenuineIntel ~2128 Mhz
[04]: Intel64 Family 6 Model 47 Stepping 2 GenuineIntel ~2128 Mhz
BIOS Version: Dell Inc. 2.3.0, 4/11/2011



Orlando Colamatteo
Orlando Colamatteo
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You've been around long enough to know "it depends" :-D

If HyperThreading is left on then I agree with keeping Max Degree of Parallelism below 32 in any conceivable scenario. If you were only considering the 32 physical cores when choosing 16 then great. But if you chose 16 after considering all 64 CPUs then I would drop it to 8.

All stories about enabling and HyperThreading seem to be anecdotal at best. I have seen having it enabled help, hinder and make no impact at all. The only way to know will be to test with your workload.

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Indianrock
Indianrock
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Guess I was looking for that "easy" button. We can test in production, on Sunday, but don't have a good tool to apply a typical business day load.



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