Re: git and time

[Linus Torvalds <torvalds@osdl.org>]

On Wed, 27 Sep 2006, Linus Torvalds wrote:
> 
> No, it's actually much deeper than that.
> 
> To git, pure replication simply isn't an action at all, so trying to track 
> it would be like trying to track all the voices in my head - something 
> that doesn't exist. It wouldn't be "truth", it would be insanity.

Another reason it's not an action at all: git in many ways does not 
actually care at all about the difference of a "local branch" and a 
"remote branch on another host".

Of course there _is_ a difference, in that the remote branch has to be 
fetched from that other repository, but it's possible (and some of the 
original design came from this) to share the repository data between 
multiple separate repositories. They can even be on different machines, if 
there is a networked filesystem in between (and, unlike most systems, the 
git database format should even be happy about _disconnected_ networked 
filesystems).

So git from the ground up is designed so that there is no real difference 
between "remote branch" and "local branch", other than simply physically 
where the data might be.

By that token, "cloning" a repository is pretty much by definition a 
no-op as far as the repository contents is concerned. In fact, if you use 
"git clone -l -s", all the cost is just checking out the new copy (so if 
you add "-n" to avoid checking out the new state, you basically have a 
zero-cost clone).

	[torvalds@g5 ~]$ time git clone -n -l -s v2.6/linux empty-clone

	real    0m0.129s
	user    0m0.084s
	sys     0m0.048s

That's it. I created a "clone" of the whole kernel repo in 0.129 seconds.

Exactly because cloning doesn't actually _do_ something (of course, 0.129 
seconds in git speak is pretty slow, so I suspect we are doing something 
stupid here with shell-script).

		Linus