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Re: More shared buffers causes lower performances

From: Greg Smith <gsmith(at)gregsmith(dot)com>
To: Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com>
Cc: pgsql-performance <pgsql-performance(at)postgresql(dot)org>
Subject: Re: More shared buffers causes lower performances
Date: 2007-12-26 18:23:58
Message-ID: Pine.GSO.4.64.0712261316580.11546@westnet.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Wed, 26 Dec 2007, Guillaume Smet wrote:

> 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 stole the graph idea from Mark Wong's DBT2 code and one of these days 
I'll credit him appropriately.

> 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

Ah, now this is really interesting, as it rules out all the write 
components and should be easy to replicate even on a smaller server.  As 
you've already dumped a bunch of time into this the only other thing I 
would suggest checking is whether the same behavior also happens on 8.2 on 
your server.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD

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