[Dovecot] High level of pop3 popping causing server to become unresponsive

[Root Kev]

During the last time that the load went up, it became unable to login / su
to root for the entire period that dovecot was running, we had to kill
dovecot and go back to Popa3d until the mailq was cleared up.  We are
running CentOS 5.6 server.  Based on TOP running at the time the CPU usage
was running under 10%.  Once Dovecot was killed, we were then able to log
in /su again.

We were under the impression that checking to shadow directly should be the
fastest and least amount of overhead, is any of the other ways to connect
have less load on authentication to PAM?

Thanks,

Kevin

On Thu, May 17, 2012 at 4:57 PM, Timo Sirainen <tss at iki.fi> wrote:

> On 17.5.2012, at 18.22, Root Kev wrote:
>
> > We have put Dovecot 2.1.4 on several of our production servers (CentOS,
> on
> > Dell R710, with 20GB memory, dual CPU Quad-core). We have a single
> instance
> > of Dovecot running and currently have several instances of Popa3d.  When
> > there are significant amount of popping from 2 mailboxes that dovecot
> that
> > is popping from (500+ msgs in the mailboxes), the popping of the messages
> > causes the boxes to become unresponsive.  We use another application that
> > connects to the Dovecot, downloads 2-10 messages, then processes them,
> then
> > sends the delete command to Dovecot.
>
> Unresponsive for a long time?.. What CentOS version?
>
> > When this issue occurs we are unable to become Root, or login again if we
> > close our ssh connection.  This only occures when Dovecot is doing the
> > popping.  If we only run the older Popa3d, this doesn't occur.  We
> believe
> > it is caused by the way dovecot is authenticating.
>
> Sounds like PAM is hanging. Is the (CPU) load in general high at this time?
>
> > We are using auth_mechanisms = plain
> >
> > passdb
> > drive = shadow
> >
> > usedb
> > driver = passwd
> > args = blocking=yes
>
> Using shadow/passwd directly shouldn't affect PAM at all. So this is a
> rather strange problem..