On 07/13/2010 10:35 AM, Andras Fabian wrote:
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 :-)
It looks to me that vm.zone_reclaim_mode value is related to NUMA machines that
have "local" memory per node and shouldn't be used at all in your environment.
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
--
Stephen Clark
NetWolves
Sr. Software Engineer III
Phone: 813-579-3200
Fax: 813-882-0209
Email: steve.clark@xxxxxxxxxxxxx
www.netwolves.com
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