On Mon, Jan 19, 2004 at 03:47:38PM +0100, Bart Dumon wrote:
> i'm running qpopper 4.0.5 on linux (2.4.x) with maildir patch
> (0.12) and pam_radius for authentication.
>
> right now, i'm suffering from high cpu load averages once it's
> gets too busy the load will skyrocket to abnormal high values
> and the service will become unavailable untill it's restarted.
> this typically happens during peak times when we receive 15 pop
> sessions/sec.
>
> at first it thought it was radius related because i'm seeing the
> following error message during the peak times:
>
> Jan 19 14:07:41 xxx popper[13404]: pam_radius_auth: RADIUS server x.x.x.x failed to
> respond
>
> but even with a more performant radius, the problem persists, it
> looks like the radius errors are a consequence of the problem and
> not the real cause.
> everything is pointing in the direction of the amount of pop sessions
> whenever you get to the 13-14pops/sec barrier, qpopper seems to
> be giving up. it's not traffic related because the amount of traffic
> is higher outside the peak hours.
Usually this kind of overload is due to many users having large
mailboxes (e.g. 30MB and up) in the old UNIX mbox format. In this
format, the file needs to be recopied to update the messages' status
when popped, which results in the POP sessions completely saturating
your disk I/O bandwidth.
I have also seen some Radius daemons show a tendency to die under
this type of heavy load.
I haven't seen reports of this with maildir format. However, what
you're describing is consistent with I/O bandwidth saturation.
If you are saturating your disk bandwidth, you'll see a large number
of concurrent tasks waiting to run ("load" as shown by the uptime
command or xload) but a high proportion of idle time shown by vmstat.
At that point you'll need to try to figure out why all this bandwidth
is still going on even with maildir format; I don't use that patch, so
I can't help with troubleshooting it.
-- Clifton
--
Clifton Royston -- [EMAIL PROTECTED]
Tiki Technologies Lead Programmer/Software Architect
Did you ever fly a kite in bed? Did you ever walk with ten cats on your head?
Did you ever milk this kind of cow? Well we can do it. We know how.
If you never did, you should. These things are fun, and fun is good.
-- Dr. Seuss
