Ok, treshold=100 practically disables compacting for non-fully deletable volumes. After this deleting fully deletable volumes is quick. But it disables threshold based partial compacting, which then needs to be run separately.
How does Duplicati behave in a situation where I run compact separately, and just kill it based on timer? If the application is working securely in segmented transactions. That should work. If not, something will break and create corruption or situation which requires manual cleanup (sigh).
Actually I could test run this case. Starting and killing compaction with large data set with random kill time to see if it breaks. Yet, if it’s known it works well, there’s no need for testing. Who let the chaos monkeys lose?