[Dovecot] Maildir "locking"

[Attila Nagy]

On 09/15/11 11:43, Timo Sirainen wrote:
> On Thu, 2011-09-15 at 11:37 +0200, Attila Nagy wrote:
>>> So you have a proxy that decides what backend server the connections are
>>> redirected to? How about you do it completely without locking with
>>> dsync? Moving between servers works basically the same as converting a
>>> mailbox format, with the difference of "changing mail_location" you
>>> "change backend server".
>>> http://wiki2.dovecot.org/Tools/Dsync#example_converting
>>>
>> Yes, there is a proxy in front of the servers. Is dsync usable with 3rd
>> party maildir programs? (not only Dovecot uses these mailboxes)
> The problems with 3rd party maildir programs come if during the move
> they:
>
>   - Expunge last message(s) from mailbox. (dsync can't know if it should
> add or expunge them, so it plays it safe and adds them back)
>
>   - Delete a mailbox. (dsync can't know if it should add or delete it, so
> again it just adds it back.)
>
>   - Remove subscriptions. (again pretty much the same reason.)
>
> It's probably quite unlikely that they do any of this during the move.
> You could even reduce the window by doing:
>
> 1. dsync backup
> 2. dsync backup
> 3. switch to new server
> 4. kill all existing connections
> 5. dsync mirror
>
> The 3-5 steps probably take only a few seconds. The "dsync backup" then
> guarantees that the destination server will look exactly like the source
> server. ("dsync mirror" is used in step 5, because between steps 3-4
> either server can get changes.)
>
OK, thanks for the info, I will try it out.