Re: 8.3 on FreeBSD 6.3, sudden performance degradations

On Mon, 8 Sep 2008, Ivan Zolotukhin wrote:

> Yep, update_process_title = off if it is important.

Have you considered turning it on so you can see what processes are most
involved in the spike? Normally in your situation I'd try to capture what
the output from top was during the problem period and match that with what
the processes involved are doing at the time, and you'll need that to see
inside the PG processes. If the event is random then this data can be
hard to capture, you might have to write some scripts to save top output
in batch mode and the output from ps.

Did you confirm that the slow periods aren't checkpoint-related? I've
seen some wacky stuff on Linux before where the system percentage went up
dramatically because the background disk I/O process got hyperactive.
Again, the way you can usually figure that out is to look at what top is
showing during that period. I suspect you'll find some daemon going
crazy. The vmstat and iostat info you included are certainly strange but
I don't know enough about FreeBSD to know exactly what would cause that.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD