Tips re syncing notmuch database and maildir via iCloud?

[Olly Betts]

On Mon, Jan 15, 2024 at 08:35:37PM -0400, David Bremner wrote:
> HGV <hgv at fastmail.com> writes:
> 
> > Does anyone have experience syncing the notmuch database or an entire 
> > maildir directory via iCloud? I keep most of my email archive offline 
> > but since iCloud added end-to-end encryption, I've considered syncing my 
> > archived mail and notmuch database via iCloud. But I'm worried that 
> > iCloud might introduce issues either directly with the notmuch database 
> > or by slightly altering the mail files/directories. Any tips about 
> > syncing the notmuch database or a maildir directory (whether iCloud or 
> > via another service) would be appreciated.
> 
> Since you didn't get any answer on the notmuch list, I'm forwarding your
> mail to the Xapian list. I guess if Xapian syncs fine in general to
> iCloud, notmuch should be likely (but not guaranteed) OK.

I know nothing about iCloud, but assuming it syncs the filenames and
contents correctly then the potential concerns I can see if you're
syncing a Xapian database are:

* On the machine being synced from you need to ensure that indexing
  doesn't happen during syncing or else the synced version may be
  corrupted - if you run "notmuch new" in a mail delivery hook or
  from cron or similar that's problematic

* On the side being synced to searches may fail or work incorrectly
  during syncing

Xapian's replication feature knows how to sync changes safely avoiding
these potential problems, but I've no idea if you could make it work
with iCloud.

Cheers,
    Olly