Re: Joining cg-*-id

[Petr Baudis <pasky@suse.cz>]

Dear diary, on Tue, Sep 20, 2005 at 04:53:11PM CEST, I got a letter
where Linus Torvalds <torvalds@osdl.org> told me that...
> On Tue, 20 Sep 2005, Petr Baudis wrote:
> > > 
> > > So I'd love to have
> > > 
> > > 	git diff yesterday..
> > > 
> > > but the fact is, there's no sensible semantics for it. _which_ yesterday? 
> > > There might be five different points that are "close to 24 hours ago", 
> > > along five different paths backwards in the history.
> > 
> > A well-defined meaning for this from Cogito standpoint would be "the
> > last commit on our HEAD before the date and all commits committed and
> > merged to the HEAD". In Cogito, you don't merge two branches _together_,
> > you merge one branch _into_ another (represented by the parents order),
> > so this would be sensible.
> 
> No, it's _not_ sensible or well-defined.
> 
> The order of the parents does not matter. It fundamentally _cannot_ 
> matter. I realize that both git and cogito put the "primary parent" first, 
> but that doesn't help one iota - because git is distributed, if the other 
> side merged and we just did a fast-forward, the "primary parent" will be 
> the _other_ side.
> 
> In other words, anybody who thinks that the order of parents is meaningful 
> is in for some nasty shocks. It really _fundamentally_ isn't true. I 
> realize that's hard to accept, but it's a truism in a distributed system. 
> You really cannot have parent ordering and distribution at the same time.

Ok ok. I can now remember already learning about this once, but I forgot
again. I should write it down into some README for myself or so, I
guess. ;-) Sorry about the noise.

I'll just drop the date revision specifier support from Cogito. I don't
know if any measurable number of people actually use it in the real
world anyway.

-- 
				Petr "Pasky" Baudis
Stuff: http://pasky.or.cz/
VI has two modes: the one in which it beeps and the one in which