Re: Recovering from repository corruption

From: Jakub Narebski <jnareb@gmail.com>
Date: Jun 10, 2008, 17:55 UTC
Message-ID: <m3abhtp42o.fsf@localhost.localdomain>
In-Reply-To: <6dbd4d000806101026m458513ecqa8141f509bad7602@mail.gmail.com>

"Denis Bueno" <dbueno@gmail.com> writes:

Show 15 quoted lines

> I was told in the thread above that I could use grafts and "git
> filter-branch" to create a new repository that simply got rid of the
> offending object.  That case was simpler, as it was the initial import
> of a file that had only two commits total that was corrupted.
> However, in this case there are changes between the initial and latest
> version of the file, and commits between the corrupted versions, so, I
> can imagine that it would be hard to get rid of in-between commits.
> 
> The thing that makes sense intuitively (read: not as a Git expert, but
> as a user) is to just let me replace the commits associated with the
> problematic objects with new versions of those commits (e.g. make
> change described in the commit message, which is different from the
> actual change that was recorded, due to whitespace/formatting issues).
>  Is this what I should do?  And to do so, should I be reading chapter
> 5 of the manual?

Without checking Git User's Manual, I think the solution could go as the following.

Assume that history looks like this

    ...---.---a---*---b---.---...

where by '*' is marked corruped commit (commit shich tree contains corrupted blobs).

First, you can check the commit message for '*' using git-cat-file or git-show, you can get the difference between 'a' and 'b' using "git diff a b". When you know how repaired commit 'X' should look like, do something like:

  $ git checkout -b <temp-branch> 'a'
  $ <edit edit edit>
  $ git commit

Then history would look like this

    ...---.---a---*---b---.---...
               \
                \-X

Now with grafts make 'b' be a child of 'X', i.e. modify parent of 'b' for history to look like below:

    ...---.---a---*   b---.---...
               \     /
                \-X-/

Examine history using git-log, git-show, check tree with git-ls-tree and examining files, use graphical history browser like gitk.

Then if possible use git-filter-branch to make history recorded in grafts file permanent...

HTH

-- 
Jakub Narebski
Poland
ShadeHawk on #git