Hi Greg, hmmm, thats true. Thos settings for example were much higher too (on the Ubuntu server), than on our old machine. New machine has: - dirty_ratio = 20 (old has 10) - dirty_background_ratio = 10 (old has 5) But obviously setting vm.zone_reclaim_mode=0 "fixes" the problem to (which was "1" on new machine and "0" on old). See my latest post to Craig. I hope using vm.zone_reclaim_mode=0 doesn't have other dire consequences :-) Andras Fabian -----Ursprüngliche Nachricht----- Von: Greg Smith [mailto:greg@xxxxxxxxxxxxxxx] Gesendet: Dienstag, 13. Juli 2010 16:29 An: Andras Fabian Cc: Craig Ringer; Tom Lane; pgsql-general@xxxxxxxxxxxxxx Betreff: Re: PG_DUMP very slow because of STDOUT ?? Andras Fabian wrote: > So the kernel function it is always idling on seems to be congestion_wait ... Ugh, not that thing again. See http://www.westnet.com/~gsmith/content/linux-pdflush.htm ; that chunk of code has cost me weeks worth of "why isn't the kernel writing things the way I asked it?" trouble in the past. I know the kernel developers have been fiddling with pdflush again recently, they might have introduced yet another bug into how it handles heavy write volume. You can reduce dirty_ratio and dirty_background_ratio to try and improve things, but the congestion code will thwart any attempt to make them really low. You might monitor what shows up as "Dirty:" in /proc/meminfo to see if that lines up with the slow periods; example of what bad output looks like at http://notemagnet.blogspot.com/2008/08/linux-write-cache-mystery.html -- Greg Smith 2ndQuadrant US Baltimore, MD PostgreSQL Training, Services and Support greg@xxxxxxxxxxxxxxx www.2ndQuadrant.us -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
