Re: [PATCH] pack-objects: use of version 3 delta is now optional.

From: Nicolas Pitre <nico@cam.org>
Date: Oct 15, 2006, 18:30 UTC
Message-ID: <Pine.LNX.4.64.0610151422510.17085@xanadu.home>
In-Reply-To: <7vac3xzbze.fsf@assigned-by-dhcp.cox.net>

On Sun, 15 Oct 2006, Junio C Hamano wrote:

Show 11 quoted lines

> Nicolas Pitre <nico@cam.org> writes:
> 
> > If anything, maybe this patch can be added before v1.4.3 is released:
> >...
> > This way pack v3 could be fed to GIT v1.4.3 and above whenever we add 
> > back pack v3 generation, and a pack converted to v2 from any v3 on the 
> > fly when that capability is not present.
> 
> I think that is sensible.  I also was thinking that we should
> call the current one packv3 and the one with delta-base-offset
> packv4.

I think we should not. The pack version should be tied to incompatible pack data to prevent older GIT versions from misinterpreting newer packs. The delta block copy encoding is a perfect example of that where a bit changed meaning.

The delta-base-offset case included a new object type that wasn't used before hence there is no room for confusion, and yet that new delta object could be encoded according to pack version 2 or pack version 3 which makes it orthogonal to the pack version itself.

Nicolas