Re: [REVISED PATCH 2/6] Introduce commit notes

["Shawn O. Pearce" <spearce@spearce.org>]

Junio C Hamano <gitster@pobox.com> wrote:
> I've long time ago concluded that if we care about reliability
> (and we do very much), a bisectable tree without breaking
> backward compatibility is impossible.  I was hoping to find a
> "hole" in tree object format so that I can place an extended
> section that is invisible to older versions of git, and place a
> table that records offsets of each tree entries to help
> bisection and/or perhaps a hash table to help look-up, but I do
> not think it is possible.
...
> But the tree object format
> is designed so tight that I do not see there is any place to put
> an extension section.

I came to the same conclusion the last time I thought about this
problem, for all the same reasons you outlined.  And came up with
pack v4.  Because the only way I could see that we could produce
a more optimal tree was to just use a different *compression* of
the tree, while still keeping its data the same.  Nico seemed to
agree at the time, because he worked on the prototype with me.  :-)

Its still hanging around in my fastimport repository.  But has not
been merged with any recent Git, and it still needs a lot of work.

-- 
Shawn.