Re: Bad objects error since upgrading GitHub servers to 1.6.1

From: Junio C Hamano <gitster@pobox.com>
Date: Jan 28, 2009, 01:06 UTC
Message-ID: <7vvds0z1c1.fsf@gitster.siamese.dyndns.org>
In-Reply-To: <bab6a2ab0901271634x7201130bx4a565bd8bea6967b@mail.gmail.com>

PJ Hyett <pjhyett@gmail.com> writes:

Show 13 quoted lines

>> As we do not know what version github used to run (or for that matter what
>> custom code it adds to 1.6.1), I guessed that the previous one was 1.6.0.6
>> and did some comparison.  The client side pack_object() learned to take
>> alternates on the server side into account to avoid pushing objects that
>> the target repository has through its alternates, so it is not totally
>> unexpected the client side changes its behaviour depending on what the
>> server does.
>
> The only custom code we've written was a patch to git-daemon to map
> pjhyett/github.git to a sharded location (eg.
> /repositories/1/1e/df/a0/pjhyett/github.git) instead of the default.
>
> The new alternates code in 1.6.1 sounds like that could be the issue.

It could be.

With the old server, when project A has a forked project A1, and A1 borrows (via alternates) objects from A, pushing into A1 did not look at refs in A's repository (this all happens on the server end).

With the new server, the server side also advertises the tips of A's branches as commits that are fully connected, when the client side tries to push into A1. Older clients ignored this advertisement, so when they pushed into A1, because their push did not depend on what's in repository A on the server end, did not get affected if repository A (not A1) is corrupted. A new client talking to the server would be affected because it believes what the server says.

Older client ignores this advertisement, so if you are seeing trouble reports from people who use older clients, then you can dismiss this conjecture as unrelated. But if you see the issue only from people with new clients, this could be just exposing a repository corruption of A (not A1) on the server end that people did not know about before.