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Message-ID: <162867790712260912p1e00dd75yfaebf6fffe6d2403@mail.gmail.com>
Date: Wed, 26 Dec 2007 18:12:21 +0100
From: "Pavel Stehule" <pavel.stehule@gmail.com>
To: "Guillaume Smet" <guillaume.smet@gmail.com>
Subject: Re: More shared buffers causes lower performances
Cc: "Simon Riggs" <simon@2ndquadrant.com>,
	pgsql-performance <pgsql-performance@postgresql.org>,
	"Stefan Kaltenbrunner" <stefan@kaltenbrunner.cc>
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Hello

I tested it and it is true. In my configuration 1GRam, Fedora 8, is
PostgreSQL most fast with 32M shared buffers :(. Diff is about 5% to
256M

Regards
Pavel Stehule

On 26/12/2007, Guillaume Smet <guillaume.smet@gmail.com> wrote:
> On Dec 26, 2007 12:21 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
> > bgwriter_lru_maxpages = 0
> >
> > So we can see if the bgwriter has any hand in this?
>
> It doesn't change the behaviour I have.
>
> It's not checkpointing either as using pgbench-tools, I can see that
> tps and latency are quite stable during the entire run. Btw, thanks
> Greg for these nice tools.
>
> I thought it may be some sort of lock contention so I made a few tests
> with -N but I have the same behaviour.
>
> Then I decided to perform read-only tests using -S option (pgbench -S
> -s 100 -c 16 -t 30000 -U postgres bench). And still the same
> behaviour:
> shared_buffers=64MB : 20k tps
> shared_buffers=1024MB : 8k tps
>
> Any other idea?
>
> --
> Guillaume
>
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