Re: Recovering from missing objects?

Geert Uytterhoeven [off-list ref] writes:

	Hi all,

I start to see suspicious messages about missing objects in one of my working
repositories:

| vixen$ git gc
| error: Could not read c406ab0be69c912ea59233595a071478103cdad8
| fatal: bad tree object c406ab0be69c912ea59233595a071478103cdad8
| error: failed to run repack
| vixen$ 

My setup:
  - I have one reference repository (cloned from Linus' linux-2.6.git)
  - I have several working repositories, cloned using --reference to my
    reference repository. A working repository has several remotes (cloned from
    other Linux kernel repositories).

I always do a `git pull' in the reference repository, before doing a `git
remote update' in a working repository. When I do `git gc' in a working
repository, it cleans up all objects that are not in the reference repository.
Hence I only need to care about backup of the .git directories in the working
repositories (the stuff I'm working on), and not about the reference
repository (its objects are publicly available and replicated all over the
world).

I identified the missing object listed above to be part of a remote repository.
Doing a `git remote update' doesn't fetch it again, as git is too smart and
thinks I already have everything.

If I clone the remote repository, I have the object in the new clone.
However, how do I get the missing object back into the .git directory of my
working repository?

In the new clone:

	$ IT=c406ab0be69c912ea59233595a071478103cdad8
	$ TYPE=$(git cat-file -t $IT)
        $ git cat-file $TYPE $IT >/var/tmp/$IT.raw

Go to the repository that lacks the object and then

	$ git hash-object -t $TYPE -w --stdin </var/tmp/$IT.raw

After that you may find objects that $IT needs to reference.  You can
obviously repeat the above procedure until you have nothing missing.


I also suspect you could do this instead; I haven't thought things through
and that is why I say "suspect" but this is safe (i.e. not destructive)
and may worth a try.

In the new clone:

	$ IT=c406ab0be69c912ea59233595a071478103cdad8
	$ H=$(git rev-list --objects $IT | git pack-objects mine)
        $ mv mine-$H.pack /var/tmp

Go to the repository that lacks the object and then

	$ git unpack-objects </var/tmp/mine-$H.pack