[Dovecot] Dotlock dovecot-uidlist errors / NFS / High Load

[list at airstreamcomm.net]

On Mon, 24 Jan 2011 08:41:31 -0600, <list at airstreamcomm.net> wrote:
> Timo,
> 
> Thanks for the quick reply!  We are building an rpm with the patch and
> will test this week and report back with our findings.
> 
> We are grateful for your help and the chance to communicate directly
with
> the author of dovecot!
> 
> Michael
> 
> On Thu, 20 Jan 2011 23:18:16 +0200, Timo Sirainen <tss at iki.fi> wrote:
>> On Thu, 2011-01-20 at 08:32 -0600, list at airstreamcomm.net wrote:
>> 
>>> Created dotlock file's timestamp is different than current time
>>> (1295480202 vs 1295479784): /mail/user/Maildir/dovecot-uidlist
>> 
>> Hmm. This may be a bug that happens when dotlocking has to wait for a
>> long time for dotlock. See if
>> http://hg.dovecot.org/dovecot-1.2/raw-rev/9a50a9dc905f fixes this.

Timo,

We tested the patch you suggested with no success.  We are seeing
timestamps straying into the 100's of seconds of difference, which does not
reflect the perceivable drift that shows on our systems clock (which is
negligible, sub 1 second).  Currently we run against two stratum 2 servers
that get their time from two stratum 1 servers, and per Stan's suggestions
earlier we are rebuilding the stratum 2 machines on bare metal hardware
(not in a virtual machine) to be sure the clocks will be super stable.  I
guess what I am asking is if you have ever seen an issue similar to this
and if NTP actually played a role.  I have spent some time reviewing the
mailing list archives and have not found a definitive answer from other
Dovecot user's experiences. 

Thanks again,

Michael

Here's the error showing a difference of 239 seconds:

Created dotlock file's timestamp is different than current time
(1295900137 vs 1295899898): /mail/username/Maildir/dovecot-uidlist

Here's the output of dovecot -n after patching:

# 1.2.16: /etc/dovecot.conf
# OS: Linux 2.6.18-92.el5 x86_64 CentOS release 5.5 (Final) 
protocols: imap pop3
listen(default): *:143
listen(imap): *:143
listen(pop3): *:110
shutdown_clients: no
login_dir: /var/run/dovecot/login
login_executable(default): /usr/libexec/dovecot/imap-login
login_executable(imap): /usr/libexec/dovecot/imap-login
login_executable(pop3): /usr/libexec/dovecot/pop3-login
login_process_per_connection: no
login_process_size: 128
login_processes_count: 4
login_max_processes_count: 256
login_max_connections: 386
first_valid_uid: 300
mail_location: maildir:~/Maildir
mmap_disable: yes
dotlock_use_excl: no
mail_nfs_storage: yes
mail_nfs_index: yes
mail_executable(default): /usr/libexec/dovecot/imap
mail_executable(imap): /usr/libexec/dovecot/imap
mail_executable(pop3): /usr/libexec/dovecot/pop3
mail_plugin_dir(default): /usr/lib64/dovecot/imap
mail_plugin_dir(imap): /usr/lib64/dovecot/imap
mail_plugin_dir(pop3): /usr/lib64/dovecot/pop3
auth default:
  username_format: %Ln
  worker_max_count: 50
  passdb:
    driver: pam
  userdb:
    driver: passwd