flags not synced correctly with dovecot sync (dsync)

[Dan Christensen]

I should add that these problems arise frequently in practice, even if
changes are only being made on a single machine, e.g. laptop1.  Flag
changes on laptop1 propagate to server, but then are reverted on server
when laptop2 syncs with server, and then are reverted on laptop1 when it
syncs again with server.  If I redo the flag changes on laptop1, the
process just repeats and they are removed again.

Suggestions for debugging are very welcome, as currently syncing is
much too unreliable for me to continue using it.

Dan

On Feb 16, 2019, Dan Christensen via dovecot <dovecot at dovecot.org> wrote:

> I'm running dovecot 2.3.4.1 from https://repo.dovecot.org/ on Ubuntu
> 18.04 on three machines that I'll call server, laptop1 and laptop2.
>
> Both laptop1 and laptop2 run dovecot sync against server to keep local
> copies of my imap folders.  Even when I initially had only two machines,
> laptop1 and server, I occasionally noticed that flags were lost, usually
> custom flags used by Gnus, but I couldn't reliably reproduce the
> problem.
>
> Now that I have two laptops syncing against the server, the problem has
> gotten worse and I figured out a way to reproduce it:
>
> - on server: create new IMAP folder test, and put two read messages in it
> - on laptop1:  doveadm sync -u user -l 10 -m test -f user at server
> - on laptop2:  doveadm sync -u user -l 10 -m test -f user at server
>
> At this point, all three machines show the two messages M1 and M2
> as being read.
>
> - on laptop1: mark message M1 unread
> - on laptop2: mark message M2 unread
> - on laptop1:  doveadm sync -u user -l 10 -m test -f user at server
>   Both laptop1 and server have M1 unread, M2 read, as expected.
> - on laptop2:  doveadm sync -u user -l 10 -m test -f user at server
>   Now laptop2 and server have M1 *read*, M2 unread.
> - on laptop1:  doveadm sync -u user -l 10 -m test -f user at server
>   Now laptop1 and the server have both M1 and M2 *read*.
> - on laptop2:  doveadm sync -u user -l 10 -m test -f user at server
>   Now laptop2 has both read as well.
>
> The two lines that say "*read*" are wrong in my opinion.  dsync
> propagated a read mark to an unread message, even though that message
> was marked unread more recently than it was marked read.
>
> I usually use stateful sync, and get many related problems.
> I just did a test in which M1 and M2 started out read, and I
> started with empty files named dstate.test on laptop1 and laptop2.
> Then I did the above procedure, using the command
>
> doveadm sync -u user -l 10 -m test -s "`cat dstate.test`" user at server > dstate.test
>
> At the end, laptop2 and server had both messages unread (which is good),
> but laptop1 had only M1 unread, and repeated runs of the sync command
> did not correct this.  So the stateful sync failed to detect a change.
>
> Are these bugs in dovecot?  Is there more information that I can
> provide?  The output of doveconf -n on one machine is below, and
> the others are almost identical.
>
> Thanks for any help!
>
> Dan
>
> # 2.3.4.1 (3c0b8769e): /etc/dovecot/dovecot.conf
> # OS: Linux 4.15.0-45-generic x86_64 Ubuntu 18.04.1 LTS 
> # Hostname: laptop2
> auth_mechanisms = plain login
> listen = 127.0.0.1
> mail_index_log2_max_age = 10 days
> mail_index_log_rotate_min_age = 1 days
> mail_index_log_rotate_min_size = 300 k
> mail_location = maildir:~/Maildir
> namespace inbox {
>   inbox = yes
>   location = 
>   mailbox Drafts {
>     special_use = \Drafts
>   }
>   mailbox Junk {
>     special_use = \Junk
>   }
>   mailbox Sent {
>     special_use = \Sent
>   }
>   mailbox "Sent Messages" {
>     special_use = \Sent
>   }
>   mailbox Trash {
>     special_use = \Trash
>   }
>   prefix = 
> }
> passdb {
>   args = scheme=CRYPT username_format=%u /etc/dovecot/users
>   driver = passwd-file
> }
> protocols = imap
> service imap-login {
>   inet_listener imap {
>     address = *
>     port = 143
>   }
>   inet_listener imaps {
>     address = *
>     port = 943
>     ssl = yes
>   }
> }
> service imap {
>   process_limit = 25
> }
> ssl_cert = </etc/dovecot/private/dovecot.pem
> ssl_client_ca_dir = /etc/ssl/certs
> ssl_dh = # hidden, use -P to show it
> ssl_key = # hidden, use -P to show it
> userdb {
>   args = username_format=%u /etc/dovecot/users
>   driver = passwd-file
> }
> protocol lda {
>   postmaster_address = [elided]
> }
> protocol imap {
>   mail_max_userip_connections = 20
> }