Re: how to remove unreachable objects?

[Jeff King <peff@peff.net>]

On Mon, Sep 19, 2011 at 11:08:31AM +0200, dieter@schoen.or.at wrote:

> this is my use case:
> i create a repository and produce several commits on master.
> then i go back to a certain tag and create a new branch, where i also
> commit.
> then i switch back to master and delete (-D) the other branch.
> it should now be unreachable from within git (to prove its existence,
> i remember a commit SHA1 on the dead branch).

It will still be referenced by the HEAD reflog, won't it?

> git checkout master
> git branch -D $DEAD
> git show $dead_commit
> git fsck --unreachable --full --verbose

This shows it reachable, because it is connected from the HEAD reflog.

> git fsck --unreachable HEAD \
>                     $(git for-each-ref --format="%(objectname)" refs/heads)

And this shows it as unreachable, because you are asking git to only
look at the branch tips and HEAD (by default, it looks at all refs and
reflogs).

I suspect you copied this straight from the git-fsck manpage. That
advice is a bit outdated, I think. It blames (in some form) all the way
back to the original documentation added in c64b9b8 (2005-05-05, only a
few weeks after git was born). A few weeks later, fsck learned to
default to looking at all refs (1024932, 2005-05-18). And then other
sane defaults like reflogs got tacked on later (reflogs came around the
1.4.x era, in 2006).

> git fsck --lost-found
> git prune -v $dead_commit
> git prune $(git rev-parse --all)
> git repack
> git prune-packed
> git gc --prune=now
> git gc --aggressive
> git show $dead_commit

If you really want to make it unreachable, you should expire the
reflogs, too:

  git reflog expire --expire=now --all
  # will now report unreachable
  git fsck --unreachable
  # will now actually delete objects
  git prune -v
  # gives "bad object ..."
  git show $dead_commit

git-gc will do this for you, but of course the default expiration time
is much longer (I think something like 90 days).

-Peff