Re: Seeking performance advice and explanation for high I/O on 8.3

On Thu, Sep 3, 2009 at 4:16 PM, Scott Otis<scott(dot)otis(at)intand(dot)com> wrote:
> Sorry about not responding to the whole list earlier - this is my first time posting to a mailing list.
>
> Would providing more information about the size and complexities of the databases help?
>
> I measure I/O stats with iostat - here is the command I use:
>
> iostat -d -x mfid0 -t 290 2
>
> I tried looking at the man page for iostat but couldn't find anywhere how to determine what the stats are for sequential vs random - any help there?
>
> When using 'top -m io' the postgres stats collector process is constantly at 99% - 100%.
>
> When using 'top' the WCPU for the postgres stats collector and the autovacuum process are constantly at 20% - 21%.
>
> Is that normal?  It seems to me that the stats collector is doing all the I/O (which would mean the stats collector is doing 46.1 megabytes /sec).
>
> Also, the I/O stats don't change hardly at all (except at night during backups which makes sense).  They don't go up or down with user activity on the server - which makes me wonder a little bit.  I have a feeling that if I just turned off Apache that the I/O stats wouldn't change.  Which leads me to believe that the I/O is not query related - its stats collecting and autovacuuming related.  Is that expected?
>
> It seems to me that the stats collector shouldn't be using that much I/O and CPU (and the autovacuum shouldn't be using that much CPU)  - therefore something in my configuration must be messed up or could be changed somehow.  But maybe I'm wrong - please let me know.
>
> I don't think my setup is necessarily slow.  I just want to make it as efficient as possible and wanted to get some feedback to see if am setting things up right.  I am also looking out into the future and seeing how much load I can put on this server before getting another one.  If I can reduce the I/O and CPU that the stats collector and autovacuum are using without losing any functionality then I can put more load on the server.
>
> Again thanks for all the help.

Can you post to the list all the uncommented lines from your
postgresql.conf file and attach the results of "select * from
pg_stat_all_tables" as an attachment?

...Robert