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
