Message-ID: <50744A95.9020403@optionshouse.com>
Date: Tue, 9 Oct 2012 11:02:29 -0500
From: Shaun Thomas <sthomas@optionshouse.com>
Reply-To: <sthomas@optionshouse.com>
Organization: Peak6
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To: Craig James <cjames@emolecules.com>
CC: <pgsql-performance@postgresql.org>
Subject: Re: Two identical systems, radically different performance
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On 10/08/2012 06:40 PM, Craig James wrote:

> Nobody has commented on the hyperthreading question yet ... does it
> really matter? The old (fast) server has hyperthreading disabled, and
> the new (slower) server has hyperthreads enabled.

I doubt it's this. With the newer post-Nehalem processors, 
hyperthreading is actually much better than it was before. But you also 
have this:

CPU    Speed    L3 Cache  DDR3 Speed
E5606  2.13Ghz  8MB       800Mhz
E5620  2.4Ghz   12MB      1066Mhz

Even with "equal" threads, the CPUs you  have in the new server, as 
opposed to the old, are much worse. The E5606 doesn't even have 
hyper-threading, so it's not an issue here. In fact, if you enabled it 
on the old server, it would likely get *much faster*.

We saw a 40% improvement by enabling hyper-threading. Sure, it's not 
100%, but it's not negative or zero, either.

Basically we can see, at the very least, that your servers are not 
"identical." Little things like this can make a massive difference. The 
old server has a much better CPU. Even crippled without hyperthreading, 
I could see it beating the new server.

One thing you might want to check in the BIOS of the new server, is to 
make sure that power saving mode is disabled everywhere you can find it. 
Some servers come with that set by default, and that puts the CPU to 
sleep occasionally, and the spin-up necessary to re-engage it is 
punishing and inconsistent. We saw 20-40% drops in pgbench pretty much 
at random, when CPU power saving was enabled.

This doesn't cover why your IO subsystem is slower on the new system, 
but I suspect it might have something to do with the memory speed. It 
suggests a slower PCI bus, which could choke your RAID card.

-- 
Shaun Thomas
OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604
312-444-8534
sthomas@optionshouse.com

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