[Dovecot] Replication plans

[Timo Sirainen]

On Fri, 2007-05-18 at 12:20 -0400, Bill Boebel wrote:
> So what about tackling this replication problem from a different
> angle...  Make it Dovecot's job to replicate the index and control
> files between servers, and make it the file system's job to replicate
> just the mail data.  This would require further disconnecting the
> index and control files from the mail data, so that there is less
> syncing required.  i.e. remove the need to check directory mtimes and
> to compare directory listings against the index; and instead assume
> that the indexes are always correct.  Periodically you could still
> check to see if a sync is needed, but you'd do this must less
> frequently.

This would practically mean that you want either cydir or dbox storage.

This kind of a hybrid replication / clustered filesystem implementation
would simplify the replication a bit, but all the difficult things
related to UID conflicts etc. will still be there. So I wouldn't mind
implementing this, but I think implementing the message content sending
via TCP socket wouldn't add much more code anymore.

The clustered filesystem could probably be used to simplify some things
though, such as UID allocation could be done by renaming a "uid-<next
uid>" file. If the rename() succeeded, you allocated the UID, otherwise
someone else did and you'll have to find the new filename and try again.
But I'm not sure if this kind of a special-case handling would be good.
Unless of course I decide to use the same thing for non-replicated
cydir/dbox.

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