On Fri, 9 Oct 2009, Alan McKay wrote: > Hey folks, > > CentOS / PostgreSQL shop over here. > > I'm hitting 3 of my favorite lists with this, so here's hoping that > the BCC trick is the right way to do it :-) > > We've just discovered thanks to a new Munin plugin > http://blogs.amd.co.at/robe/2008/12/graphing-linux-disk-io-statistics-with-munin.html > that our production DB is completely maxing out in I/O for about a 3 > hour stretch from 6am til 9am > This is "device utilization" as per the last graph at the above link. You make no mention of the file system that you are currently using here either. If you look and see I/O wait rather high than your file system could also be the culprit. EXT3/4 journalling is terrible under heavy load because the kjournald is single threaded. We have a user here that completely saturates a 4 core 8GB memory machine with only a few clients because it can't keep up with the journal writes. Are you seeing any high I/O waits and lots of kjournald's running? -- James A. Peltier Systems Analyst (FASNet), VIVARIUM Technical Director HPC Coordinator Simon Fraser University - Burnaby Campus Phone : 778-782-6573 Fax : 778-782-3045 E-Mail : jpeltier at sfu.ca Website : http://www.fas.sfu.ca | http://vivarium.cs.sfu.ca http://blogs.sfu.ca/people/jpeltier MSN : subatomic_spam at hotmail.com Does your OS has a man 8 lart? http://www.xinu.nl/unix/humour/asr-manpages/lart.html