Re: Summer of Code 2008 project application draft: Pack v4

From: Shawn O. Pearce <spearce@spearce.org>
Date: Mar 31, 2008, 04:12 UTC
Message-ID: <20080331041217.GE10274@spearce.org>
In-Reply-To: <20080329205046.GA27926@bohr.gbar.dtu.dk>

Peter Eriksen <s022018@student.dtu.dk> wrote:

> Here is a draft of my application for the Google Summer of Code 2008.

...

Show 13 quoted lines

> The project goal is to rebase the code and ideas developed for the
> version 4 of the git pack format, which showed good promise of making
> packs smaller, and faster.
> 
> The ideas of a new even more optimized pack format has been floating
> around the git world for almost two years, and because of the rapid pace
> of development the code implementing those ideas has become less, and
> less ready for inclusion in mainline.
> 
> Since those patches touch so many of the core functions in git, it will
> be a good chunk of work getting them mergeable, and nobody has gotten
> around to doing that yet. This will be a good oppertunity for laying the
> ground work, and getting the ball rolling again.

Have you had a chance to look at those patches yet? Or the code that they touch, but which has been heavily modified since then (like say builtin-pack-objects.c)?

I would hope that forward-porting those patches would only take us through to about the mid-term, and then finishing out the bulk of the series (like commit dict encoding, maybe dict of object ids used in trees) would be the remainder of the summer. But that may be aggressive. To be successful I think the student working on this project needs to spend some time during the bonding period to understand the current pack v2 format and how the pack v4 format was going to address some of the shortcomings of v2.

To some extent I have left the design details about pack v4 off
the ideas page hoping to draw students into explaining their own
ideas for how to improve upon Git's pack data storage.  Even if the
student's ideas provide less compression than pack v4 was hinting
it can give us, it shows the student's ability to think through
the problem and their desire to work on the project.  Its also why
I called it "v4/v5"... some of the students own ideas may be novel
to us and better than v4, hence creating a v5...

-- 
Shawn.