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Re: Effects of setting linux block device readahead size

From: Matthew Wakeling <matthew(at)flymine(dot)org>
To: "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Effects of setting linux block device readahead size
Date: 2008-09-15 16:18:38
Message-ID: alpine.DEB.1.10.0809151717001.23198@aragorn.flymine.org (view raw or flat)
Thread:
Lists: pgsql-performance
On Thu, 11 Sep 2008, Scott Carey wrote:
> Preliminary summary:
> 
> readahead  |  8 conc read rate  |  1 conc read rate
> 49152  |  311  |  314
> 16384  |  312  |  312
> 12288  |  304  |  309
>  8192  |  292  |
>  4096  |  264  |
>  2048  |  211  |
>  1024  |  162  |  302
>   512  |  108  |
>   256  |  81  | 300
>     8  |  38  |

What io scheduler are you using? The anticipatory scheduler is meant to 
prevent this slowdown with multiple concurrent reads.

Matthew


-- 
And the lexer will say "Oh look, there's a null string. Oooh, there's 
another. And another.", and will fall over spectacularly when it realises
there are actually rather a lot.
         - Computer Science Lecturer (edited)

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Subject: Re: Effects of setting linux block device readahead size
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Subject: Re: select on 22 GB table causes "An I/O error occured while sending to the backend." exception

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