Newbie question about replication

[John Fawcett]

On 18/10/2020 22:53, Piotr Auksztulewicz wrote:
> On Sat, Oct 17, 2020 at 11:17:34PM +0200, John Fawcett wrote:
>>> I have observed my mail storage directories on both instances and have
>>> noticed that they diverge a little over time - the instance B not having
>>> all the updates. However the moment I connect another client to instance
>>> B and log in as a particular user, the state on instance B springs to the
>>> correct state and I see the same content on both clients, and the storage
>>> directories become identical as well.
>> Are there any replication errors logged? Does doveadm replicator status or
>> doveadm replicator status <mailbox> give any sign of errors?
>>
>> Can you give some example or evidence of the disalignment that is happening?
> Thank you for response. I was asking if such difference in directories is
> normal or not and do I have the approach right or is there some obvious error
> in my configuration.
>
> I still have an example that prompted me to write this email. Instance B had
> three mails missing in comparison to instance A, when I listed the storage
> directories from the command line. They got replicated fine just after I
> connected a client to instance B. No difference since then, but I need to
> observe the servers for some more time, it seems like it happens over a few
> weeks or so. No errors in dovecot logs, doveadm replicator status output does
> not show any errors as well, but instances have been restarted, so it is not
> a goof indication. I am going to enable debug to see what's going on. Maybe it
> was some transient situation or human error on my part during setting it all up
> or tweaking the configuration. I will come back if I observe such thing again.
>
> Here are the listings. Hostnames etc. replaced for privacy.
>
> --- Instance A
> root at serverA:/var/vmail/user at example.net/mail/INBOX/.MailDir/cur# ll
> total 14684
> drwx------ 2 vmail vmail    4096 Oct 16 13:15  .
> drwx------ 5 vmail vmail    4096 Oct 16 13:15  ..
> -rw------- 1 vmail vmail  303371 Oct 30  2019 '1572438988.M167729P10012.hostname.mydomain.net,S=303371,W=307546:2,S'
> -rw------- 1 vmail vmail 1789790 Oct 30  2019 '1572438998.M633142P10012.hostname.mydomain.net,S=1789790,W=1814325:2,S'
> -rw------- 1 vmail vmail  171191 Nov 17  2019 '1574012316.M188507P14607.hostname.mydomain.net,S=171191,W=173557:2,S'
> -rw------- 1 vmail vmail 3430888 Nov 29  2019 '1574956300.M308957P25339.hostname.mydomain.net,S=3430888,W=3475534:2,S'
> -rw------- 1 vmail vmail    7185 Mar 14  2020 '1584150674.M740366P21925.hostname.mydomain.net,S=7185,W=7294:2,S'
> -rw------- 1 vmail vmail    5543 Mar 25  2020 '1585148832.M609262P877.hostname.mydomain.net,S=5543,W=5674:2,S'
> -rw------- 1 vmail vmail    3052 Apr 19 22:23 '1587327803.M423484P19471.hostname.mydomain.net,S=3052,W=3122:2,S'
> -rw------- 1 vmail vmail   13690 Apr 23 14:47 '1587646046.M939301P22621.hostname.mydomain.net,S=13690,W=13886:2,S'
> -rw------- 1 vmail vmail 8917623 May 25 19:06 '1590426395.M585516P47979.hostname.mydomain.net,S=8917623,W=9033467:2,S'
> -rw------- 1 vmail vmail    5473 Jun 20 20:14 '1592676840.M810974P68188.hostname.mydomain.net,S=5473,W=5576:2,S'
> -rw------- 1 vmail vmail    8776 Jun 21 19:25 '1592760350.M765525P68795.hostname.mydomain.net,S=8776,W=8936:2,S'
> -rw------- 1 vmail vmail    4624 Jul 23 17:25 '1595517903.M310464P9504.hostname.mydomain.net,S=4624,W=4715:2,S'
> -rw------- 1 vmail vmail    4378 Aug 18 00:16 '1597702561.M109036P34930.hostname.mydomain.net,S=4378,W=4453:2,S'
> -rw------- 1 vmail vmail   14522 Sep 17 11:52 '1600336372.M982371P3862.hostname.mydomain.net,S=14522,W=14813:2,S'
> -rw------- 1 vmail vmail   30411 Sep 23 14:43 '1600865025.M865916P104.hostname.mydomain.net,S=30411,W=30850:2,S'
> -rw------- 1 vmail vmail   39928 Sep 30 08:27 '1601447231.M21429P464.hostname.mydomain.net,S=39928,W=40487:2,S'
> -rw------- 1 vmail vmail    8529 Oct  9 15:32 '1602250379.M823144P212.hostname.mydomain.net,S=8529,W=8701:2,S'
> -rw------- 1 vmail vmail   17972 Oct 15 00:59 '1602716371.M291521P5700.hostname.mydomain.net,S=17972,W=18407:2,S'
> -rw------- 1 vmail vmail   38528 Oct 15 08:24 '1602743049.M23930P5928.hostname.mydomain.net,S=38528,W=39224:2,S'
> -rw------- 1 vmail vmail   52350 Oct 15 12:05 '1602756328.M324186P6101.hostname.mydomain.net,S=52350,W=53436:2,S'
> -rw------- 1 vmail vmail  112458 Oct 16 13:05 '1602846323.M415371P7147.hostname.mydomain.net,S=112458,W=114768:2,S'
>
>
> --- Instance B
> root at serverB:/var/vmail/user at example.net/mail/INBOX/.MailDir/cur# ll
> total 14608
> drwx------ 2 vmail vmail   12288 Oct 16 13:15  .
> drwx------ 5 vmail vmail    4096 Oct 16 13:15  ..
> -rw------- 1 vmail vmail  303371 Oct 30  2019 '1572438988.M167729P10012.hostname.mydomain.net,S=303371,W=307546:2,S'
> -rw------- 1 vmail vmail 1789790 Oct 30  2019 '1572438998.M633142P10012.hostname.mydomain.net,S=1789790,W=1814325:2,S'
> -rw------- 1 vmail vmail  171191 Nov 17  2019 '1574012316.M188507P14607.hostname.mydomain.net,S=171191,W=173557:2,S'
> -rw------- 1 vmail vmail 3430888 Nov 29  2019 '1574956300.M308957P25339.hostname.mydomain.net,S=3430888,W=3475534:2,S'
> -rw------- 1 vmail vmail    7185 Mar 14  2020 '1584150674.M740366P21925.hostname.mydomain.net,S=7185,W=7294:2,S'
> -rw------- 1 vmail vmail    5543 Mar 25  2020 '1585148832.M609262P877.hostname.mydomain.net,S=5543,W=5674:2,S'
> -rw------- 1 vmail vmail    3052 Apr 19 22:23 '1587327803.M423484P19471.hostname.mydomain.net,S=3052,W=3122:2,S'
> -rw------- 1 vmail vmail   13690 Apr 23 14:47 '1587646046.M939301P22621.hostname.mydomain.net,S=13690,W=13886:2,S'
> -rw------- 1 vmail vmail 8917623 May 25 19:06 '1590426395.M585516P47979.hostname.mydomain.net,S=8917623,W=9033467:2,S'
> -rw------- 1 vmail vmail    5473 Jun 20 20:14 '1592676840.M810974P68188.hostname.mydomain.net,S=5473,W=5576:2,S'
> -rw------- 1 vmail vmail    8776 Jun 21 19:25 '1592760350.M765525P68795.hostname.mydomain.net,S=8776,W=8936:2,S'
> -rw------- 1 vmail vmail    4624 Jul 23 17:25 '1595517903.M310464P9504.hostname.mydomain.net,S=4624,W=4715:2,S'
> -rw------- 1 vmail vmail    4378 Aug 18 00:16 '1597702561.M109036P34930.hostname.mydomain.net,S=4378,W=4453:2,S'
> -rw------- 1 vmail vmail   14522 Sep 17 11:52 '1600336372.M982371P3862.hostname.mydomain.net,S=14522,W=14813:2,S'
> -rw------- 1 vmail vmail   30411 Sep 23 14:43 '1600865025.M865916P104.hostname.mydomain.net,S=30411,W=30850:2,S'
> -rw------- 1 vmail vmail   39928 Sep 30 08:27 '1601447231.M21429P464.hostname.mydomain.net,S=39928,W=40487:2,S'
> -rw------- 1 vmail vmail   38528 Oct 15 08:24 '1602743049.M23930P5928.hostname.mydomain.net,S=38528,W=39224:2,S'
> -rw------- 1 vmail vmail  112458 Oct 16 13:05 '1602846323.M415371P7147.hostname.mydomain.net,S=112458,W=114768:2,S'
>
Hi Piotr

can you check if the missing emails are in the new directory on host B?

My guess is that the missing emails appeared on host A in new and were
replicated to host B in new. Then the imap client connected to host A
moved them from new to cur on host A and that such movement is not
subject to replica. So long as the emails have been replicated to either
new or cur on host B, then it should not be an issue about losing emails
if host A goes down, since connecting an imap client to host B will move
the emails to cur (that is no replication involved).

John