git svn clone/fetch hits issues with gc --auto

Hi folks,

Long time no see! Importing a 3GB (~25K revs, tons of files) SVN repo I hit the gc error:

warning: There are too many unreachable loose objects; run 'git prune' to remove them. gc --auto: command returned error: 255

I don't seem to be the only one -- https://stackoverflow.com/questions/35738680/avoiding-warning-there-are-too-many-unreachable-loose-objects-during-git-svn

Looking at code history, it dropped the ability to pass options to git repack when it was converted it to using git gc.

Experimentally I find that tweaking it to run git gc --auto --prune=5.minutes.ago works well, while --prune=now breaks it. Attempts to commit fail with missing objects.

- Why does --prune=now break it? Perhaps "gc" runs in the background,
and races with the commit being prepared?

- Would it be safe, sane to apply --prune=some.value on _clone_?

- During _fetch_, --prune=some.value seems risky. In a checkout being
actively used for development or merging it'd risk pruning objects
users expect to be there for recovery. Would there be a safe, sane
way?

- Is there a safer, saner value than 5 minutes?

cheers,

m