[Duplicity-talk] inc backup if nothing changed

[duplicity-talk]

Hi,

I want to re-raise a question that wasn't finally answered in 
https://bugs.launchpad.net/duplicity/+bug/768481.

I have the same use case as described in the bug above.
In my case I running a backup of my photo collection (folder structured 
by year). I am running one duplicity backup per year. By nature former 
years changing rarely, but they my change if I revisit some photos and 
add tags etc.
Therefore I want to make sure all changes get into a backup regularly 
(weekly).

As described even if nothing has changed in a folder a incremental 
backup is created and a few bytes are stored.

I am unsure about the logic in duplicity. Why is there a small sigtar 
even if nothing has been changed?

The workaround to do a --dry-run and check for changes may work, but it 
requires a 2nd run though the filesystem if there are changes to do the 
backup. With thousands of files and hundreds of GB per year, this is not 
a lightweight job.
It would be great if this can be avoided.

Is there any technical reason why this incremental back need to get 
pushed even if not files was changed?
What impact could have an option like "--skip-empty-backup"?

Thanks
  Thomas