On 02/20/13 19:14, Josh Berkus wrote:
>> Sounds to me like your IO system is stalling on fsyncs or something
>> like that. On machines with plenty of IO cranking up completion
>> target usuall smooths things out.
> It certainly seems like it does. However, I can't demonstrate the issue
> using any simpler tool than pgbench ... even running four test_fsyncs in
> parallel didn't show any issues, nor do standard FS testing tools.
>
We were really starting to think that the system had an IO problem that we
couldn't tickle with any synthetic tools. Then one of our other customers who
upgraded to Ubuntu 12.04 LTS and is also experiencing issues came across the
following LKML thread regarding pdflush on 3.0+ kernels:
https://lkml.org/lkml/2012/10/9/210
So, I went and built a couple custom kernels with this patch removed:
https://patchwork.kernel.org/patch/825212/
and the bad behavior stopped. Best performance was with a 3.5 kernel with
the patch removed.
--
Jeff Frost <jeff@pgexperts.com>
CTO, PostgreSQL Experts, Inc.
Phone: 1-888-PG-EXPRT x506
FAX: 415-762-5122
http://www.pgexperts.com/