Skip site navigation (1) Skip section navigation (2)

Re: More shared buffers causes lower performances

From: "Merlin Moncure" <mmoncure(at)gmail(dot)com>
To: "Guillaume Smet" <guillaume(dot)smet(at)gmail(dot)com>
Cc: pgsql-performance <pgsql-performance(at)postgresql(dot)org>, "Stefan Kaltenbrunner" <stefan(at)kaltenbrunner(dot)cc>
Subject: Re: More shared buffers causes lower performances
Date: 2007-12-29 17:22:00
Message-ID: b42b73150712290922k3b22739tc564134c591fa28a@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Dec 25, 2007 7:06 PM, Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com> wrote:
> While monitoring the server with vmstat, I can't see any real reason
> why it's slower. When shared_buffers has a higher value, I/O are
> lower, context switches too and finally performances. The CPU usage is
> quite similar (~50-60%). I/O doesn't limit the performances AFAICS.

Can you confirm that i/o is lower according to iostat?  One
possibility is that you are on the cusp of where your server's memory
covers the database and the higher buffers results in lower memory
efficiency.

If raising shared buffers is getting you more page faults to disk,
this would explain the lower figures regardless of the # of syscalls.
If your iowait is zero though the test is cpu bound and this
distinction is moot.

merlin

In response to

pgsql-performance by date

Next:From: Sebastián BaioniDate: 2008-01-02 12:24:03
Subject: Re: [GENERAL] Can't make backup
Previous:From: Guillaume SmetDate: 2007-12-29 10:38:40
Subject: Re: More shared buffers causes lower performances

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group