[Duplicity-talk] how does duplicity decide which files are "new" or "changed"?

[Michael Hellwig]

Hi everyone,

the reason I'm asking is that I'm seeing a problem where duplicity will,
on each run, decide that a huge amount of files are "new" and re-backup
them. To wit:

https://paste.in-ulm.de/?c54aee5ea3557034#UmwzH2kvCe/1sy4PaZTkQu2rRuxjSh4Jfb8fJEQv7sg=

this the output of two subsequent runs of duplicity on the same homedir
on your bog-standard run of the mill linux server. This is the homedir
of a person who seldom logs in via ssh, mostly has email on it plus a
few things that are sent there for storage purposes via rsync. Email is
accessed via a few parallel methods, namely
* local mutt installation (sometimes for checking/fixing things)
* dovecot -> roundcube webmail
* dovecot -> kaiten mail (android client)
* dovecot -> thunderbird

the size of the email maildir is 3 GB. All other files are backups from
e.g. the mobile phone or the laptop and get never changed, never
deleted, only ever added to (via rsync).

Nevertheless, I run duplicity twice on the same day and as the above
paste shows, duplicity decides _each_time_ that 5177 (more than five
thousand) files are "new" and that it needs to create an additional
7.something GB of backup (which it then dutifully transfers across the
network, yay). Every. Single. Time.

So. What am I doing wrong? How do I even find out what I'm doing wrong?
Am I doing something wrong?

The command line is just
duplicity /home/username scp://address@hidden//home/other_user/backups/