Re: git-log to go forward instead of reverse?

From: Linus Torvalds <torvalds@osdl.org>
Date: Jul 10, 2006, 19:20 UTC
Message-ID: <Pine.LNX.4.64.0607101212410.5623@g5.osdl.org>
In-Reply-To: <863bd9p9en.fsf@blue.stonehenge.com>

On Mon, 10 Jul 2006, Randal L. Schwartz wrote:

Show 6 quoted lines

> 
> Linus> Well, as long as you realize that that automatically means that you
> Linus> have to walk the whole commit list, and you won't be able to get the
> Linus> incremental output that git-log and friends normally are able to give?
> 
> Wow.  Yes, I think I can live with that for the application.

It's a big deal for me, I often end up doing things like

	git log -p some-random-file

to see what has happened, and getting the most recent changes basically instantaneously (rather than waiting for the thing to traverse all of the history) is a big deal.

If you have a fairly small archive, or you don't use pathname limiting, the history generation is so fast that you'll never even notice. But with the kernel, doing something like

	git log drivers/serial

takes just over two seconds for me, and if I had to wait for two seconds before the first data starts arriving, I'd go nuts.

To see this in cold hard numbers:

	// Full log
	[torvalds@g5 linux]$ time git log drivers/serial > /dev/null

	real    0m2.267s
	user    0m2.204s
	sys     0m0.020s

	// Simulate "get the first screenful"
	[torvalds@g5 linux]$ time git log drivers/serial | head -25 > /dev/null

	real    0m0.054s
	user    0m0.048s
	sys     0m0.008s

	// Simulate "get the first screenful of reverse output"
	[torvalds@g5 linux]$ time git log --reverse drivers/serial | head > /dev/null

	real    0m2.218s
	user    0m2.176s
	sys     0m0.044s

and it's the difference between the second and the third case I wanted to point out.

The difference between getting the first screenful in 0.054 seconds versus it taking 2.218 seconds is quite noticeable, and one of the things I've actually spent a fair amount of time on is to make sure that the incremental output case is the _common_ one for all the normal operations like "git log -p".

			Linus