[Dovecot] dsync - one or two ways?

[Timo Sirainen]

On Sat, 2009-07-18 at 01:43 +0200, joakim at verona.se wrote:
> Timo Sirainen <tss at iki.fi> writes:
> 
> > On Fri, 2009-07-17 at 22:31 +0200, joakim at verona.se wrote:
> >> This sounds really awesome! How testable is it?
> >
> > By "testable" do you mean "is it working now"? It should work except for
> > mailbox deletions and renames. But I haven't really tested it, just ran
> > unit tests. :) And it pretty much requires using Dovecot v2.0 for IMAP
> > so that it can handle expunges properly. And I wouldn't really recommend
> > doing that yet..
> 
> Would this setup work then?
> - dovecot 1.2 on master and slave machines
> - dsync on the slave machine, 2 way sync
> - propagate expunges by some other means, like removing maildir mail
> files with unison or similar?

Actually there shouldn't be problems with expunges after all. Conflicts
just are detected less reliably. For example if:

Server 1 saves message with UID=123
Server 2 saves a different message with UID=123
Server 1 expunges messages UID=123

dsync is run to move changes from server 2 to server 1. It notices that
"oh, UID=123 has been expunged from server 1 already" and server 2's
UID=123 message isn't copied there. Or if you're syncing changes from 1
to 2, it would expunge the UID=123 from server 2.

If server 1 had been running Dovecot v2.0, the expunge record would have
message's GUID stored and dsync would notice that there was a GUID
conflict and copy the server 2's message to server 1 as UID=124.

> How would I handle mailbox addition, renaming and deletions?

The reason why dsync can't do that without Dovecot v2.0 is because it
can't be done reliably without storing extra information.. (And I
haven't yet even implemented that to v2.0.) So the answer is: Not
easily.
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