On Tuesday, August 20 at 03:24 PM, quoth Leon Waldman:
Do any one have any inputs or caveats in store the Maildir folders
on dropbox to sync them between different computers?
I think the caveat is going to be race conditions; and given that
Dropbox can be used offline, the race conditions can be quite easy to
trigger. There is no inherent tracking of unique messages in Maildir
folders. Imagine the relatively simple situation where you receive a
new message. In location A you read it, and in location B you delete
it. As long as you haven't had a full A sync followed by a full B sync
BEFORE you delete that message, you can run into trouble (imagine B's
dropbox client does a scheduled sync before A does, so B will wait a
full refresh timeout before it will see the changes to A).
Reading the email causes the underlying mail file to be renamed, which
means that the delete operation on the slower (temporarily un-sync'd)
host will be reversed, and your message will magically re-appear.
However, since it shows back up marked as "read", not only will it be
easy for you to not notice, it will be easy for mutt to not notice
(don't worry, mutt will notice eventually).
Since Dropbox can be used offline as well as online, imagine the same
thing happening where A is offline when you read the message (it
queues up the "delete file X, store file X.newname" operations), and
comes back online sometime after you deleted the message in location
B. Changes to the mail directory done on A will supersede operations
done on location B in unexpected ways. As another example, imagine
that on location B, instead of delete the message, you reply to it.
Replying causes another rename operation, which means that after a
full sync, you will have two copies of that message: one marked read,
and the other marked "replied".
So okay, maybe Maildir isn't the right storage technique, how about
Mbox? This is an even bigger problem, because in situations like I
just described, the entire MAILBOX will be duplicated (by Dropbox
itself), because Dropbox has no real way of handling change conflicts
in the internals of files (all files, to them, are binary blobs, not
text blocks whose changes can be merged).
The fact of the matter is that Dropbox is not designed for frequently
changing data, or for handling even slightly-overlapping
synchronization issues ESPECIALLY of filesystem meta-data, such as
file names and directories, which Maildir relies on for correct
operation. In terms of how it technically functions, Dropbox can be
better thought of as an on-line backup system: synchronization
operations are not instantaneous, and has only rudimentary conflict
resolution mechanisms.
On the other hand, such synchronization issues (and worse) are EXACTLY
what IMAP was designed to handle.
~Kyle
--
As far as the laws of mathematics refer to reality, they are not
certain, and as far as they are certain, they do not refer to reality.
-- Albert Einstein
