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From: Tomas Vondra <tv@fuzzy.cz>
To: pgsql-performance@postgresql.org
Subject: Re: Two identical systems, radically different performance
Date: Tue, 09 Oct 2012 01:16:15 +0200
Message-ID: <50735EBF.5010909@fuzzy.cz> (raw)
In-Reply-To: <CAFwQ8reOc-ntKsLRSqVOf81FsGRA_OiVbusDduB2BuH_SzdNGQ@mail.gmail.com>
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On 9.10.2012 01:03, Craig James wrote:
> 
> 
> On Mon, Oct 8, 2012 at 3:50 PM, Claudio Freire <klaussfreire@gmail.com
> <mailto:klaussfreire@gmail.com>> wrote:
> 
>     On Mon, Oct 8, 2012 at 7:48 PM, Craig James <cjames@emolecules.com
>     <mailto:cjames@emolecules.com>> wrote:
>     >> >  # 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.
> 
>     Is the read-ahead the same in both systems?
> 
> 
> Yes, as I said in the original reply (it got cut off from your reply):
> "Same on both servers."

And what about read-ahead settings on the controller? 3WARE used to have
a read-ahead settings on their own (usually there are three options -
read-ahead, no read-ahead and adaptive). Is this set to the same value
on both machines?

Tomas




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