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@xxxxxxxxxxxxx> CTO, PostgreSQL Experts, Inc. Phone: 1-888-PG-EXPRT x506 FAX: 415-762-5122 http://www.pgexperts.com/ -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
