Re: Tracking branch history

From: Linus Torvalds <torvalds@osdl.org>
Date: May 13, 2006, 00:03 UTC
Message-ID: <Pine.LNX.4.64.0605121656350.3866@g5.osdl.org>
In-Reply-To: <Pine.LNX.4.64.0605121640210.3866@g5.osdl.org>

On Fri, 12 May 2006, Linus Torvalds wrote:

Show 8 quoted lines

> 
> IOW, a good (?) way to do it is to literally have a commit hook that 
> basically just does
> 
> 	echo $new >> .git/$branch-commit-history
> 
> possibly together with a datestamp thing (ie it could be something like
> "echo $new "$USER" $(date)" rather than just the commit SHA1).

Btw, the real problem with this is how to use it.

The only really valid use I see is to use it for date-based things, ie if given a date, look up the most recent commit ID that is older than the date in question. No other op seems to really make sense, but that one does.

Now, the one other operation that is semantically sensible is to use the list of commits to figure out a "path" through the commit space. However, that path won't actually even be well-defined (a fast-forward pull/merge can and often /will/ update the history in a way where it's impossible to select one particular path to the previous commit listed in the commit log).

The other thing that makes the "path" thing hard is that it's just fundamentally a pretty hard thing to calculate, even when it would result in one unambiguous path. I _believe_ that it comes close to what "git bisect" does, and that the bisect algorithm could probably be used to always create _a_ path between each commit (is just pick successive half-way-points - the commit list _should_ always have a direct dominance relationship, but the bisection algorithm should do something half-way sane even if you "jump about" by "git reset" or something).

It might be interesting to see if it's somethign that can be done reasonably efficiently.

			Linus