Related to #6289:

When investigating that, I also ran borg compact --threshold=0 REPO and it still kept the segments full of DELs.

So, my current guess about that would be that hints -> compact is incomplete and does not hint to all segments where stuff could be compacted (== where PUTs exist that are DELeted in later segments).

Possible solutions:

• borg check --repair + borg compact maybe? check whether this completely recomputes the hints file contents.
• modify borg compact so it unconditionally runs over all segments (that would be a quite I/O heavy operation, rewriting all not-deleted segment content to new segments)