[Dovecot] New mailbox format

[John Peacock]

Timo Sirainen wrote:
> While the maildir format itself is simple, it's actually really
> difficult to handle correctly when the maildir is changing under us.
> Files can be renamed at any time so you'll have to be prepared to look
> for the file's new name at any time. Filesystems also don't work the way
> maildir assumes they do, so you have to work around their limitations
> too.

I thought that was the point of dovecot-lda, so that you know that 
dovecot is the only process touching the message files and can update 
the indexes as things change, rather than after the fact.  Too bad you 
cannot write a portable FS hook that would fire when the directory changed.

> This could possibly be also automatically set per mailbox. If user
> always expunges all mails at a time (POP3) or never expunges (mailing
> list archives), there would be only a single file.

If you are thinking that way, it might be useful to mark mailboxes as 
either:

	a) sequential access (most POP3 and archives);
	b) random access (IMAP).

and provide different tuning based on usage expectations, rather than 
trying to actively tune.  Then the system admin could choose which fits 
their needs best; we only have a few people using POP3 and everyone else 
is IMAP, and I frankly don't care what kind of performance the POP3 
people have.

> I think SQL database as a mail store would have much worse performance
> than with any filesystem based mail store.

Except that with clustering, you could have multiple DB servers getting 
hit by multiple dovecot servers.  SQL could potentially scale to much 
larger environments than filesystem support.  Plus, think of all the 
neat fulltext indexing possibilities.

I suspect GMail is based on SQL... ;-)

John

-- 
John Peacock
Director of Information Research and Technology
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