[Dovecot] Dovecot development status v1.0

[Timo Sirainen]

On Mon, 2005-06-06 at 12:51 +0200, Cor Bosman wrote:
> Well, it should be possible, after all UW can do it..and if they can...;)
> To delete a file, theoretically there should be no writing necessary.
> Just unlink the file and forget about updating indexes 

It's not so simple, because the error could come at any point, even in
the middle of updating indexes. I'd have to check all write operations
and make sure they can correctly fallback to just keeping indexes in
memory.

> (btw, our indexes
> are on a seperate filesystem without quotas!). Actually it seemed dovecot
> wanted to create the dovecot-uidlist file, and barfed on not being able
> to do that. 

This is another problem. Hmm. I tried to look up some of my older
explanations for this, but couldn't. Well, here goes again:

Mails need to be assigned UIDs with IMAP. If the UIDs aren't written to
dovecot-uidlist file, it's possible that different mails will get
different UIDs between logins. This really confuses clients which have
cached mails locally.

If we assumed that:

1) When maildir filenames are sorted, the newly arrived mails come
always after old ones. Dovecot doesn't currently satisfy this
requirement even itself, if multiple mails are saved within a second.
Have to change that..

2) After user has expunged mails, there is space to write
dovecot-uidlist file.

3) No new clients try to open the mailbox between expunging and
dovecot-uidlist locking. (This requirement could be avoided by using
fcntl() or similar locking.)

Then I think it *might* work correctly.

mbox has similar problem, but the solution is much easier and can
probably be made fully working and race-free without any special
conditions.

Anyway, you can specify different directory for dovecot-uidlist
using :CONTROLDIR=path in default_mail_env.

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