Hi --
On 04.03.2012 11:44, Timo Sirainen wrote:
In dovecot-2.1 hg you can now test dsync-based replication.
Everything isn't finished yet, but it appears to work and I've
enabled
it for my @dovecot.fi mails.
I did give it a try starting some days ago, and I can confirm that you
are right,
dsync replication can be used, but there are some issues, see below.
Let me start with replicator's configuration ...
Below is a configuration for virtual user setup.
[...]
service doveadm {
# if you're using a single virtual user, set this to
# start ssh as vmail (not root)
user = vmail
}
... that led to the following complaints at start-up:
| dovecot: master: Dovecot v2.1.1 (d66568d34e40) starting up
| dovecot: doveadm: Error: Error reading configuration:
net_connect_unix(/var/run/dovecot/config) failed: Permission denied
| [...]
| (repeatedly, presumably for the number of users in userdb?)
Therefore, I modified dsync_remote_cmd ...
dsync_remote_cmd = ssh -p 1234 -l vmail %{host} doveadm dsync-server
-u%u -l%{lock_timeout} -n%{namespace}
... and used an empty 'service doveadm { }' instead. That worked, but I
would
love to run doveadm as vmail user (security), though. How should I do
that without
running into the error messages above?
Now some observations regarding replicator:
1) I see a lot of error messages whenever replicator is in action
like (although everything is being synced correctly):
| <mail.err> mail dovecot: dsync-local(test): Error: remote:
dsync-remote(test): Info: save: box=INBOX, uid=27,
msgid=<3v2jfh5kv4z...@example.tld>, size=547, from=t...@example.tld
(admin), flags=()
| <mail.info> mail dovecot: dsync-local(test): Error: remote:
dsync-remote(test): Info: flag_change: box=TEST, uid=27568,
msgid=<20120307144810.6360a74f...@example.tld>, size=435,
from=t...@example.tld, flags=(\Seen)
JFTR: I do have mail_log plugin activated.
Some testing results:
1) I ran a test by sending locally produced mails every other minute on
both servers
simultaneously. That test ran for ~5 hours. All mails became synced
correctly, and
no losses were observable, but some duplicates.
2) I did send 100 small test mails from a distant server to my
mailservers (mx1 and mx2):
a) replicator and dsync deactivated: received 100 distinct mails (57
at mx1, 43 at mx2).
b) now, replicator active: 172 mails (100 distinct, a lot of
duplicates (up to 8
incarnations of the very same mail).
Ok, 2b) is a rather 'mailbomb-like' scenario, but it worries me a
bit: One of my users
is receiving mails from a mailing list that sends individual mails
batch-wise ...
3) replicator active: 1000 mails sent ended in 4523 mails at every
server. Well, that was
a mailbomb :-)
4) replicator active: 100 (and even 1000) locally produced mails at one
server only: all
100 (and 1000 mails) became synced, prefectly well, without
duplicates.
5) replicator active: 100 locally produced mails at both servers
simultaneously: 341 mails,
thus a lot of multiple incarnations.
(This test differed from 1) because all mails were sent in one
batch.)
Final note to these tests: It doesn't matter whether sieve with
redirecting, or sieve with
redirecting and copying, or no sieve at all has been involved.
It seems to me, that whenever a larger number of mails arrive on both
servers simultaneously,
the replicator gets into trouble [1]. I am unsure if one can expect
that a replicator should
deal with such stress, though. Or?
Résumé: The overall performance of replicator is very good from my
point of view for my
conditions (handful users, average workload of roughly 1000
mails a day).
Thank you for replicator and regards,
Michael
[1] JFTR: I did similar tests in the past with dsync running from cron
every other minute
with similar results.
