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

[Timo Sirainen]

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..