Revision d699676dda5fdf0996601006c3bac2a9c077a862 authored by Linus Torvalds on 10 August 2007, 19:31:20 UTC, committed by Junio C Hamano on 10 August 2007, 21:00:25 UTC
This trivially optimizes the two-way merge case of git-read-tree too,
which affects switching branches.

When you have tons and tons of files in your repository, but there are
only small differences in the branches (maybe just a couple of files
changed), the biggest cost of the branch switching was actually just the
index calculations.

This fixes it (timings for switching between the "testing" and "master"
branches in the 100,000 file testing-repo-from-hell, where the branches
only differ in one small file).

Before:
	[torvalds@woody bummer]$ time git checkout master
	real    0m9.919s
	user    0m8.461s
	sys     0m0.264s

After:
	[torvalds@woody bummer]$ time git checkout testing
	real    0m0.576s
	user    0m0.348s
	sys     0m0.228s

so it's easily an order of magnitude different.

This concludes the series. I think we could/should do the three-way merge
too (to speed up merges), but I'm lazy. Somebody else can do it.

The rule is very simple: you need to remove the old entry if:
 - you want to remove the file entirely
 - you replace it with a "merge conflict" entry (ie a non-stage-0 entry)

and you can avoid removing it if you either

 - keep the old one
 - or resolve it to a new one.

and these rules should all be valid for the three-way case too.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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README
////////////////////////////////////////////////////////////////

	GIT - the stupid content tracker

////////////////////////////////////////////////////////////////

"git" can mean anything, depending on your mood.

 - random three-letter combination that is pronounceable, and not
   actually used by any common UNIX command.  The fact that it is a
   mispronunciation of "get" may or may not be relevant.
 - stupid. contemptible and despicable. simple. Take your pick from the
   dictionary of slang.
 - "global information tracker": you're in a good mood, and it actually
   works for you. Angels sing, and a light suddenly fills the room.
 - "goddamn idiotic truckload of sh*t": when it breaks

Git is a fast, scalable, distributed revision control system with an
unusually rich command set that provides both high-level operations
and full access to internals.

Git is an Open Source project covered by the GNU General Public License.
It was originally written by Linus Torvalds with help of a group of
hackers around the net. It is currently maintained by Junio C Hamano.

Please read the file INSTALL for installation instructions.
See Documentation/tutorial.txt to get started, then see
Documentation/everyday.txt for a useful minimum set of commands,
and "man git-commandname" for documentation of each command.
CVS users may also want to read Documentation/cvs-migration.txt.

Many Git online resources are accessible from http://git.or.cz/
including full documentation and Git related tools.

The user discussion and development of Git take place on the Git
mailing list -- everyone is welcome to post bug reports, feature
requests, comments and patches to git@vger.kernel.org. To subscribe
to the list, send an email with just "subscribe git" in the body to
majordomo@vger.kernel.org. The mailing list archives are available at
http://marc.theaimsgroup.com/?l=git and other archival sites.

The messages titled "A note from the maintainer", "What's in
git.git (stable)" and "What's cooking in git.git (topics)" and
the discussion following them on the mailing list give a good
reference for project status, development direction and
remaining tasks.
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