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

From: Linus Torvalds <torvalds@osdl.org>
Date: Oct 15, 2006, 18:57 UTC
Message-ID: <Pine.LNX.4.64.0610151150530.3952@g5.osdl.org>
In-Reply-To: <7vac3xzbze.fsf@assigned-by-dhcp.cox.net>

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

> 
> 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.

Quite frankly, I wonder if the pure "copy size extension" (aka "v3") thing is really worth it at all.

I mean, seriously, how much does it buy us? A couple of bytes per every 64kB of delta copied? And the downside is that you can't re-use the deltas with old clients and/or you have to re-create a "v2" delta at run-time from a v3 delta by inflating, fixing and deflating it.

So I would suggest:

 - call the delta-base-offset thing the "v3" pack format.

 - forget about the current "v3 delta" entirely. We might as well continue 
   to support reading it, but there's no point in actually ever generating 
   it.

In other words, I think the current situation in top-of-master is the right situation. There's simply no point in adding code to convert v3 to v2 on the fly - even if it's not rocket science, it's just not _worth_ it.

(You could also have the extended copy deltas in v3-only, and only send it to clients that you know supports it. However, the "convert to v2" format issue still rears its ugly head, and as a result I just don't think it's _ever_ worth it).

		Linus