I haven’t tried retention before, but I did today, and looked at history, and even took a stab at a code peek.
Thank you for the file log. It may explain the last deletion. We didn’t get enough version info for the others.
Current Code
(and it looks like you can get more verbose description of what it’s doing if you’re willing to file log at profile)
At 2018-07-15 05:08:17 after a backup, Duplicati thinned out versions by placing backup versions into time buckets, then thinned those when versions were too close. The thing that might be surprising is it keeps the oldest version in a bucket, which might be a good thing in itself, but also means the deletion of versions too close together runs from oldest to newest. Something’s got to go, and it might be the newest. A scan going newest to oldest might keep the newest one, then confuse people differently by deleting an older neighbor.
“Backups to consider: 2018-07-14 05:00:03, 2018-07-13 07:27:54, 2018-07-12 05:00:04, 2018-07-11 05:00:00, 2018-07-09 05:00:01, 2018-07-08 05:00:01, 2018-07-03 07:04:04, 2018-06-26 05:00:01, 2018-06-18 07:23:47, 2018-06-03 05:00:00, 2018-04-26 05:00:01, 2018-03-18 11:24:38” turns into
1W:1D bucket
2018-07-14 05:00:03, 2018-07-13 07:27:54, 2018-07-12 05:00:04, 2018-07-11 05:00:00, 2018-07-09 05:00:01
Delete 2018-07-14 05:00:03 because it’s less than a day since the delayed 2018-07-13 07:27:54
4W:1W bucket
2018-07-08 05:00:01, 2018-07-03 07:04:04, 2018-06-26 05:00:01, 2018-06-18 07:23:47, 2018-06-03 05:00:00, 2018-04-26 05:00:01, 2018-03-18 11:24:38
Delete 2018-07-08 05:00:01 because it’s less than a week since the older 2018-07-03 07:04:04
This feature has generated an amazing amount of interest, discussion, and unfortunately confusion.
Possibly the question of which direction version thinning should go in should be discussed in forum?