WARNING: THIS PATCH CAN BREAK YOUR REPO, was Re: [PATCH 2/3] Only repack active packs by skipping over kept packs.

From: Nicolas Pitre <nico@cam.org>
Date: Oct 30, 2006, 19:07 UTC
Message-ID: <Pine.LNX.4.64.0610301332440.11384@xanadu.home>
In-Reply-To: <20061029093754.GD3847@spearce.org>

On Sun, 29 Oct 2006, Shawn Pearce wrote:

> During `git repack -a -d` only repack objects which are loose or
> which reside in an active (a non-kept) pack.  This allows the user
> to keep large packs as-is without continuous repacking and can be
> very helpful on large repositories.

Something is really broken here.

Here's how to destroy your GIT's git repository.

WARNING: MAKE A COPY BEFORE TRYING THIS!  I'm serious.

First, let's make a single pack just to make things simpler and reproducible:

$ git-repack -a -f -d $ git-prune $ git-fsck-objects --full

So far everything should be fine. It's still time to make a backup copy of your .git directory if you've not done so.

Now let's create a second pack containing a subset of the existing one.

$ git-rev-list --objects v1.4.3..v1.4.3.3 | \
  git-pack-objects --stdout | \
  git-index-pack --stdin -v --keep
$ git-fsck-objects --full

At this point the repository is still fine, but the --keep to git-index-pack above will have created a file called .git/objects/pack/pack-aceb4c6394c586abaf65d76dd6cf088f50a5b806.keep and that is the source of all the trouble to come. You still can remove that file if you don't have a backup yet.

If you still want to give it the coup de grace, just do:

$ git-repack -a -d

And now you've just lost a large amount of objects. To see the extent of the dammage, just do:

$ git-fsck-objects

So... what is the --unpacked=<pack>.pack switch supposed to mean? It is not documented anywhere and it certainly doesn't produce the expected result with a repack.