Re: A look at some alternative PACK file encodings

From: linux@horizon.com <linux@horizon.com>
Date: Sep 7, 2006, 19:22 UTC
Message-ID: <20060907192230.8764.qmail@science.horizon.com>
In-Reply-To: <Pine.LNX.4.64.0609071322010.18635@xanadu.home>

> Well... I'm using object type 6 for deltas with offset reference 
> (instead of object type 7 that is delta with sha1 reference).  So 
> there is no extra bit needed and no backward compatibility breakage.

Ah, my apologies! I didn't realize that you weren't constructing a whole new pack format, or using a global flag. In this case, the overhead is already bought and paid for, so there's no point to not taking advantage of it.

And thin packs should Just Work, once the builder is taught to use type 7 objects when necessary.

> There could be of course a new object type which payload is only a sha1 
> that deltas type 6 reference. But that can be introduced at a later date 
> if it turns out to be worthwhile (i.e. the actual saving in real use 
> scenarios is worth the (small but still) added complexity).

In this case, it's only of potential benefit if there is more than one reference to an object, and figuring it out is almost certainly more trouble than it's worth. Deltas usually form long skinny chains, not high branching factor bushes.