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From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
To: pgsql-performance@postgresql.org
Subject: Re: Two identical systems, radically different performance
Date: Tue, 09 Oct 2012 12:10:54 +1300
Message-ID: <50735D7E.7000405@catalyst.net.nz> (raw)
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On 09/10/12 11:48, Craig James wrote:
> On Mon, Oct 8, 2012 at 3:44 PM, Claudio Freire <klaussfreire@gmail.com>wrote:
>
>> On Mon, Oct 8, 2012 at 7:25 PM, Craig James <cjames@emolecules.com> wrote:
>>>>> But why? What have I overlooked?
>>>> Do you have readahead properly set up on the new one?
>>>
>>>   # blockdev --getra /dev/sdb1
>>> 256
>>
>> It's probably this. 256 is way too low to saturate your I/O system.
>> Pump it up. I've found 8192 works nice for a system I have, 32000 I
>> guess could work too.
>>
> But again ... the two systems are identical.  This can't explain it.
>

Maybe check all sysctl's are the same - in particular:

vm.zone_reclaim_mode

has a tendency to set itself to 1 on newer hardware, which will reduce 
performance of database style workloads.

Cheers

Mark




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