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From: Evgeny Shishkin <itparanoia@gmail.com>
To: Claudio Freire <klaussfreire@gmail.com>
Cc: Craig James <cjames@emolecules.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Two identical systems, radically different performance
Date: Tue, 9 Oct 2012 02:46:38 +0400
Message-ID: <A62086F6-67AE-441F-85A5-9C26EF59EBC4@gmail.com> (raw)
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On Oct 9, 2012, at 2:44 AM, 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.

This, i also suggest to rebenchmark with increased wal_buffers. May be that downscale comes from wal mutex contention.



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