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

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.

Scott Otis
CIO / Lead Developer
Intand
www.intand.com