Re: importance of bgwriter_percent - Mailing list pgsql-general

Hi,

I have not tried all the settings on the big database but yeah I have tried
most of the settings and I am not seeing any performance improvement. Rather
I would say that there was a performance degradation in my case when I used
some of the settings used for small database (like decreasing
shared_buffers, checkpoint_segments etc). I am trying to change these
parameters one by one and then see how things are getting affected.

Regards,
Vinita Bansal


>From: Scott Marlowe <smarlowe@g2switchworks.com>
>To: vinita bansal <sagivini@hotmail.com>
>CC: pgsql-general@postgresql.org
>Subject: Re: [GENERAL] importance of bgwriter_percent
>Date: Fri, 01 Apr 2005 09:43:38 -0600
>
>On Fri, 2005-04-01 at 00:36, vinita bansal wrote:
> > Hi,
> >
> > I have a 64 bit Linux box with 64GB RAM and 450GB HDD. I am running a
> > benchmark on database of size 40GB using the following settings:
> > - data=writeback
>
>You might want to read this post about ext3 with writeback:
>
>http://archives.postgresql.org/pgsql-general/2005-01/msg00830.php
>
>
> > - Moved wal logs to seperate partition
> > - settings in postgresql.conf:
> >                shared_buffers = 100000
> >         work_mem = 100000
> >         maintenance_work_mem = 100000
> >         max_fsm_pages = 200000
> >         bgwriter_percent = 2
> >         bgwriter_maxpages = 100
> >         fsync = false
> >         wal_buffers = 64
> >         checkpoint_segments = 2048
> >         checkpoint_timeout = 3600
> >         effective_cache_size = 1840000
> >         random_page_cost = 2
> >         geqo_threshold = 25
> >         geqo_effort = 1
> >         stats_start_collector = false
> >         stats_command_string = false
> >         stats_row_level = false
> >         add_missing_from = false
> >
> > I am not getting good performance here as I get when I am working on a
>small
> > database of size 1GB with the following settings :
> >                 shared_buffers = 3000
> >                 checkpoint_segments = 256
> >                 checkpoint_timeout= 1800
> >                effective_cache_size= 250000
> > Rest all settings are the same as above.
>
>What is the difference in performance on the big database if you use the
>settings from the small setup instead of the ones you're using now?
>Have you tried starting there and increasing each setting some
>incremental amount to gauge the increase in performance you get from the
>changes?  Sometimes certain settings that you think will speed up the
>database will actually slow it down, and without some kind of empirical
>testing, you really don't know if the new setting is really "better" or
>not.
>
>I'm not familiar enough with the new bgwriter stuff yet to offer any
>real advice on tuning its parameters.
>

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