Date: Mon, 13 Oct 2008 17:37:53 -0400 (EDT)
From: Greg Smith <gsmith@gregsmith.com>
To: Carlos Moreno <morenopg@mochima.com>
cc: pgsql-performance@postgresql.org
Subject: Re: "Mysterious" issues with newly installed 8.3
In-Reply-To: <48F3615B.4050705@mochima.com>
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References: <48EE98FE.60100@mochima.com>
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	<48F3615B.4050705@mochima.com>
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On Mon, 13 Oct 2008, Carlos Moreno wrote:

>> Another really handy way to gauge memory speed on Linux, if there are
>> similar kernels installed on each system like your case, is to use
>> "hdparm -T".
>
> Great tip!  I was familiar with the -T switch, but was not clear on the
> notion that the figure tells you that much about the overall memory
> performance!

I wouldn't go so far as to say it tells you *much* about it, but it does 
give a fairly useful comparison figure if the kernels are basically the 
same and can help spot gross errors.  I used it a bunch when I was 
tinkering with DDR speeds and such earlier this year, it correlated fairly 
well with other memory bandwidth measurements within the same processor 
family (so far my tests suggestion results are much higher per clock on 
Intel CPUs).  Certainly of no use for comparison if one system has a 
32-bit kernel and the other 64, and results will vary depending on general 
kernel configuration (I get very different results from seemingly similar 
RedHat and Ubuntu kernels on the same system for example).

It sounds like your CPU and memory setup are all fine, which leaves your 
mystery open.  Please let us know if you find anything interesting out, 
normally an 8.3 upgrade would run faster so your situation is a bit 
curious.  The only other benchmark I'd suggest just as a sanity check is 
bonnie++, that's a bit more thorough than what hdparm -t reports.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD