[Dovecot] "Connection queue full" errors

[Jackie Hunt]

Hi all,

Our Dovecot server became non-responsive today and had to be restarted.  
We had approximately 1200 imap sessions running, and when I looked at 
the log, I found the following errors:

Jan 16 10:02:01 lamar dovecot: imap-login: Disconnected: Connection queue full: rip=75.166.40.150, lip=129.82.103.75, TLS handshake
Jan 16 10:02:01 lamar dovecot: imap-login: Disconnected: Connection queue full: rip=75.166.40.150, lip=129.82.103.75, TLS handshake
Jan 16 10:02:12 lamar dovecot: imap-login: Disconnected: Connection queue full: rip=75.166.40.150, lip=129.82.103.75, TLS handshake
Jan 16 10:02:26 lamar dovecot: imap-login: Disconnected: Connection queue full: rip=67.162.151.85, lip=129.82.103.75, TLS handshake
Jan 16 10:02:26 lamar dovecot: imap-login: Disconnected: Connection queue full: rip=129.82.100.135, lip=129.82.103.75
Jan 16 10:02:26 lamar dovecot: imap-login: Disconnected: Connection queue full: rip=71.196.217.203, lip=129.82.103.75
Jan 16 10:02:26 lamar dovecot: imap-login: Disconnected: Connection queue full: rip=129.82.100.135, lip=129.82.103.75
Jan 16 10:02:26 lamar dovecot: imap-login: Disconnected: Connection queue full: rip=129.82.100.135, lip=129.82.103.75
Jan 16 10:02:26 lamar dovecot: imap-login: Disconnected: Connection queue full: rip=129.82.218.58, lip=129.82.103.75
...

We are running v1.0.10 on AIX.  Here's the relevant configuration 
from dovecot.conf:

# Set max. process size in megabytes. 
#login_process_size = 32

# Should each login be processed in it's own process (yes), or should one
# login process be allowed to process multiple connections (no)? 
login_process_per_connection = no

# Number of login processes to keep for listening new connections.
#login_processes_count = 3

# Maximum number of login processes to create. 
#login_max_processes_count = 128

# Maximum number of connections allowed per each login process. 
#login_max_connections = 256


We are running in the high-performance mode, where each login process can
handle a number of connections.  As I understand it that means we have 
login_max_connections * login_max_processes_count available
possible logins at a given time.  That's 32K with our configuration.  That 
seems like a very high limit.  Is that what these errors are indicating?

Thanks for any insight on this,
Jackie
---
Jackie Hunt                                                       
ACNS                                    Voice:  (970) 663-3789     
Colorado State University               FAX:    (970) 491-1958
Fort Collins, CO  80523                 Email:  jackie.hunt at colostate.edu