Re: merge time

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Jul 29, 2007, 23:35 UTC
Message-ID: <alpine.LFD.0.999.0707291623160.3442@woody.linux-foundation.org>
In-Reply-To: <630183.45851.qm@web51001.mail.re2.yahoo.com>

On Sun, 29 Jul 2007, Matthew L Foster wrote:

Show 5 quoted lines

> 
> From viewing gitweb.cgi I have observed a situation where Linus creates 
> a tag, say rc1, and then he later merges changes but some subset of 
> those changes/commits show up in the list in time order as taking place 
> _before_ the rc1 tag was made even though they were merged after.

Absolutely. This is very common indeed. It's even more common with not the -rc1 tag, but a release.

When I cut a full release, that "opens the floodgates" for the merge window, and a lot of people who have committed their changes (maybe weeks or *months* before) but where the changes weren't appropriate to be merged before the merge window, will now ask me to pull.

So you may have the situation that 2.6.22 was released, but then a few days later I'll merge stuff that was actually committed two weeks before the 2.6.22 release, but was not _in_ the release.

> Do I describe a real or possible phenomenon? And does this happen 
> because the developer that made the subset of changes in question commit 
> them to his/her local repository in time order before the rc1 tag was 
> made?

Yes. I would seriously suggest you not use "gitweb" as your way to look at the repository, because you'll never see all the interactions that way.

Cloning a git repository (not necessarily the kernel, but it needs to be something with concurrent developement), and exploring it locally with "gitk" or "qgit" is a _lot_ more informative. When you see the actual history chains graphically, something that might look "odd" in gitweb (commits that look old but weren't there a few days ago) suddenly makes tons of sense.

Show 6 quoted lines

> So an external repository had the change before the rc1 tag was made but 
> Linus' repository didn't? But internally git on Linus' machine knows 
> that the gitweb.cgi displayed time order is wrong as far as the state is 
> concerned because each repository's index file keeps local track of the 
> true local state [just time isn't reconcilable], or am I missing 
> something(s)?

Well, there i sno "wrong" time. There are just "different" times. The only thing git really tracks is not actually the time (that's purely for human consumption), but the *relationship* between commits. So git really very fundmanetally just tracks things like "commit X was the parent of commit Y", and the time is really immaterial.

The time, to git, is not really different from authorship: it's very important to track when something was done, but it's really purely informational, exactly the same way the _author_ is purely informational. It has no "meaning" for git itself.

> Is it possible for gitweb.cgi to have a new view mode that 
> sorts/displays the list based on merge time for commits (the time merged 
> into Linus' or whatever repository) so the above situation doesn't 
> happen?

The public repositories don't even know what the merge time was for me. That's a purely local feature, and while I can see it in my private repository that I actually did the merge in, I don't publish that information. It's incidental, and quite frankly, it's "wrong" to care: because "Linus' tree" is really not even supposed to be special.

		Linus