Clifton,
On Tue, Jan 20, 2004 at 01:16:53PM -1000, Clifton Royston wrote:
> >
> > 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.
> >
> 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've ran qpopper 2.5x on a sparc system with 20k mailboxes, mailboxes
where up to 40mb in mbox format so i do recognize the situation. but
my current problem is totally different. there's no recopying with
the maildir patch thus reducing I/O, which is probably it's biggest
advantage for high volume sites.
> 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.
that's absolutely true, see my sample in my mail to TLP.
bart
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