Re: kernel.org now has gitweb installed

From: Linus Torvalds <torvalds@osdl.org>
Date: Apr 28, 2005, 21:40 UTC
Message-ID: <Pine.LNX.4.58.0504281432490.18901@ppc970.osdl.org>
In-Reply-To: <1114723214.2734.9.camel@localhost.localdomain>

On Thu, 28 Apr 2005, David Woodhouse wrote:

> 
> Still, using the date isn't any better. It'll give results which are
> about as random as just sorting by the sha1 of each parent.

Well, it does use real information, and it is repeatable. And I don't see why you say that the date is meaningless, when it clearly isn't. The date absolutely does have meaning.

Not having a global clock doesn't mean that clocks go away. It just means that they don't generate a total sort. They still generate a _partial_ sort, though, and it's a very valid partial sort.

The fact is, this is how the world works in real life too. Relativity doesn't make time "pointless". You still have "before" and "after" for almost all relevant events. The fact that not _all_ events can be sorted by "before" and "after", and different observers can disagree about some of the ordering does not mean that causality has gone away and that time is meaningless.

The same is true in a distributed system. Time still exists, and is still meaningful even outside the direct "causality" links implied by the parents. People probably discussed things, and there are methods of communication other than just direct parent links, and while you're not _guaranteed_ that "before" and "after" always makes sense, they definitely still exist 99% of the time.

> The best we could probably do, from a theoretical standpoint, is to look
> at the paths via each parent to a common ancestor, and look at how many
> of the commits on each path were done by the same committer.

That's quite expensive.

> Even that isn't ideal, and it's probably fairly expensive -- but it's
> pointless to pretend we can infer anything from _either_ the dates or
> the ordering of the parents in a merge.

Wrong. The date _does_ have meaning. It shows which of the parents was more recent, which indirectly is a hint about which side had more activity going on.

In other words, it _is_ meanginful. Maybe it's a _statistical_ meaning ("that side is probably the active one, because it has the last commit"), but it's a meaning.

		Linus