Re: [Evolution] Notes on Data migration Evolution 2.24.5 to 3.4.3

[Pete Biggs <pete biggs org uk>]

> Why should the backup not maintain a canonical form of all the aspects
> of a mail system vs backing up on the way in which the data is stored.
> A canonical form would have forced all versions to be able to backup and
> restore with full backwards and forwards compatibility.
> The canonical form could evolve with versioning of data forms as they
> get more complex and programs evolve.

Sorry, I didn't really address the underlying aspect of what you are
saying here.

In the dim and distant past email was held in standardised data stores -
i.e. mbox files.  It was an almost universal standard and no matter what
program you used, it could be read and modified and other programs would
still be able to work with it.  And Evolution used that standard.  To
all intents and purposes, that was the canonical form.  Then some kind
person invented MIME and the size of email messages expanded
exponentially and all of a sudden the forever canonical form was not
good enough - the files became too big, too unwieldy, too slow and
things had to change.

Similarly with configuration data - in the early days of Unix and a
single INBOX on your local system, there was no configuration necessary
- then POP, then IMAP, then Exchange all came along and something,
somewhere had to remember what the program was supposed to do.  There
was no standard for such info so every program did its own thing.  Evo
did have a canonical form of the data, it was in flat files in the
Evolution private folders, but that eventually became too slow and too
fragile, so they changed to using gconf - which is now being deprecated
in favour of dconf.

What I'm trying to say is that 20:20 hindsight is a wonderful thing -
but it is incredibly difficult to design a data storage format that is
totally impervious to future changes and is efficient enough for
everyday usage.  I'm also fairly certain that if there was a standard
for holding or exchanging account information and data between different
programs, then Evo would have embraced it.

Finally, I would just point out that the best way of maintaining email
for use on multiple systems and that is fairly impervious to changes in
version is to keep your mail on a server and access it using IMAP - that
way you don't have to worry about moving data and if the upgrade
procedure doesn't work, all you will ever have to do is to re-enter the
account configuration.

P.