From: Theodore Tso <tytso@mit.edu>
Date: Sun, 07 Sep 2008 23:41:18 GMT
Subject: Re: Alternates and push
Message-ID: <20080907234118.GA8161@mit.edu>
In-Reply-To: <7viqt9rvwm.fsf@gitster.siamese.dyndns.org>

On Sat, Sep 06, 2008 at 11:06:49AM -0700, Junio C Hamano wrote:
> We could instead redefine the semantics of the existing alternates
> mechanism.  This technically *breaks* backward compatibility, but I
> suspect it won't hurt many existing installations:
> 
>  - Declare that a freestanding object store is illegal.  In other words,
>    if a directory "$D/objects" is (1) used as $GIT_OBJECT_DIRECTORY's
>    value, (2) pointed by some repository's "alternates" file, or (3)
>    listed in $GIT_ALTERNATE_OBJECT_DIRECTORIES's value, this change makes
>    it illegal for "$D" not being a proper git repository.
> 
>    This will not break your example of your repository's object store
>    borrowing from the object store inside Linus's repository.
> 
>  - When you have "$D/objects" in alternates, start relying on "$D/refs"
>    being correct (i.e. repository $D is not corrupt).  This technically
>    makes the system slightly less robust, as we are depending on _other
>    people's_ good behaviour even more when you use alternates, but you are
>    already depending on them having good objects in $D/objects anyway, so
>    it is not a big deal.

One way that wouldn't break backwards compatibility would be to use
$D/refs if it exists, but if it isn't, fall back to existing behavior
(which is to say, only use the refs in the repository, not in the
borrowed repository/object store).  Is there a reason why this would
be problematic?

							- Ted