dovecot - May 2004 - dovecot-1.0-test8 / nfs / maildir / flags issues

Hi List,


While (bluntly) testing the prerelease version of dovecot on our  
mailfarm (just for the webmail imap) we noticed some small problems:

- While our OLD dovecot/imap drove the load to a maximum of 1 over a  
day after running, the new dovecot/imap pushes it easily to 20. This is  
mainly due to a LOT more disk activity. This is probably caused by the  
fact we a) use indexes on disk and b) there are no indexes left. I hope  
this will smooth out when most of the indexes are made.

- We notice some very strange "delete" flag things in our IMP webmail
system (working on a test environment to be more specific). The problem  
is that if you mark some messages "deleted", a lot of messages that do
NOT have "deleted" flag are also in the deleted list. Since nothing  
changed on the webmail, it must be in the way dovecot responds  
different in the new version on certain requests.

- In the dotlocking code, it seems that dovecot uses time() for it's  
internal locktime, and uses stat() to see if the file-time of the lock  
is different. Since we use nfs there might be a time-difference on the  
file creation and time() when our nfs gets "busy". This happens a lot
when the indexes are created for multiple users at the same time  
resulting in a lot of:

	May 12 08:57:44 mf1 dovecot[3763]: imap(user at domain.tld): Our dotlock  
file  
/var/mail/mounted/d/do/domain.tld/user/Maildir/.INBOX/	 
dovecot.index.log.lock was modified (1084345063 vs 1084345062),  
assuming it wasn't overridden

I am not completely sure if this interrupts imap traffic. I think this  
MIGHT be solved by storing a stat() time as the locktime instead of a  
time(), but this might be intentional.

- I patched dovecot to report its pid in syslog messages, in order to  
find the "killed by signal X" where X are mostly 11 and 6 processes.  
The pids reported do not show up in the rest of the log file, so these  
may be "disconnected" sessions? It seems that the "old"
version has the
same problem, and nobody really complained it was broken, so this isn't  
a big issue.


To clarify our setup:

We use multiple mail-frontends running dovecot that are load-balanced  
by a cisco load-balancer. We mount our mailstores from an active-active  
backend cluster, both nodes export a big partition, and take over the  
job of the other in case of a problem. This seems to go pretty smooth.  
Our users are stored in a pgsql database. In our current setup, we run  
a modified cvs version of dovecot from WAY back, to support nfs. The  
backdraw is that we can't use the newer dovecot releases, since I  
couldn't modify the source in the way I did it the first time (with a  
LOT of help from Timo :P).

If anyone has some ideas on where to look and where to test in order to  
get our problems more clear, I would be very grateful :)


Kind regards,

Maikel Verheijen
Ladot Nederland BV.

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Maikel Verheijen wrote:

| - We notice some very strange "delete" flag things in our IMP
webmail
| system (working on a test environment to be more specific). The problem
| is that if you mark some messages "deleted", a lot of messages that
do
| NOT have "deleted" flag are also in the deleted list. Since nothing
| changed on the webmail, it must be in the way dovecot responds
| different in the new version on certain requests.

Webmail applications reply (in most cases, IMP included) on PHP imap code.

When reporting problems with webmail programs, it is thus relevant to
note what version of PHP you are running, and on what platform (or even
better, if you know it: what version of libc-client it has been linked
against).

It may be that your brand-new IMP relies on a brand-new PHP linking
against an old buggy version of libc-client.

libc-client is the core engine from UW-imap, which is also used in Pine,
PHP and other projects.

~ - Jonas

- --
* Jonas Smedegaard - idealist og Internet-arkitekt
* Tlf.: +45 40843136  Website: http://dr.jones.dk/

~ - Enden er n?r: http://www.shibumi.org/eoti.htm
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On 13.5.2004, at 12:34, Maikel Verheijen wrote:
> While (bluntly) testing the prerelease version of dovecot on our  
> mailfarm (just for the webmail imap) we noticed some small problems:
Not very good idea at least until "1.0 alpha". I can still pretty  
easily make it crash and complain about corrupt indexes.
> - While our OLD dovecot/imap drove the load to a maximum of 1 over a  
> day after running, the new dovecot/imap pushes it easily to 20. This  
> is mainly due to a LOT more disk activity. This is probably caused by  
> the fact we a) use indexes on disk and b) there are no indexes left. I  
> hope this will smooth out when most of the indexes are made.
I think this is mostly because the 1.0-tests don't cache anything. The  
index files contain only message UIDs and flags, everything else  
requires opening and parsing the message file. I'll fix the caching  
once other things seem to be working.
> - We notice some very strange "delete" flag things in our IMP
webmail
> system (working on a test environment to be more specific). The  
> problem is that if you mark some messages "deleted", a lot of
messages
> that do NOT have "deleted" flag are also in the deleted list.
Since
> nothing changed on the webmail, it must be in the way dovecot responds  
> different in the new version on certain requests.
Hm.. I'm not sure about this. Maybe concurrent access breaks it  
sometimes..
> - In the dotlocking code, it seems that dovecot uses time() for it's  
> internal locktime, and uses stat() to see if the file-time of the lock  
> is different. Since we use nfs there might be a time-difference on the  
> file creation and time() when our nfs gets "busy". This happens a
lot
> when the indexes are created for multiple users at the same time  
> resulting in a lot of:
>
> 	May 12 08:57:44 mf1 dovecot[3763]: imap(user at domain.tld): Our dotlock  
> file  
> /var/mail/mounted/d/do/domain.tld/user/Maildir/.INBOX/	 
> dovecot.index.log.lock was modified (1084345063 vs 1084345062),  
> assuming it wasn't overridden
>
> I am not completely sure if this interrupts imap traffic. I think this  
> MIGHT be solved by storing a stat() time as the locktime instead of a  
> time(), but this might be intentional.
It does store and compare stat() times for that check.. There was a bug  
where Dovecot itself overwrote the lock file and caused that error, but  
it was fixed in test8 already. Maybe there's other such problems.
> - I patched dovecot to report its pid in syslog messages, in order to  
> find the "killed by signal X" where X are mostly 11 and 6
processes.
> The pids reported do not show up in the rest of the log file, so these  
> may be "disconnected" sessions? It seems that the "old"
version has
> the same problem, and nobody really complained it was broken, so this  
> isn't a big issue.
What else should there be in log file about them? Killed by signal 11  
means just that it crashed without any specific reason. Signal 6 is  
abort(), that should write the error into log file.
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On Thu, May 13, 2004 at 11:34:17AM +0200, Maikel Verheijen
wrote:
> 
> 
> - We notice some very strange "delete" flag things in our IMP
webmail
> system (working on a test environment to be more specific). The problem  
> is that if you mark some messages "deleted", a lot of messages
that do
> NOT have "deleted" flag are also in the deleted list. Since
nothing
> changed on the webmail, it must be in the way dovecot responds  
> different in the new version on certain requests.
> 
I also have this problem with 0.99 and the python 'offlineimap' script.

I can't easily reproduce it, but sometimes whole mboxes decide to be
deleted. I am trying to get an IMAP dump and see what is happening.

  C.
-- 
 charlie at rubberduck.com - Melbourne, Australia
 http://rubberduck.com/~yeled/
 PGP: 0x14AA7941 || finger yeled at lazy.spodder.com