When we taught the commit_match() mechanism to pay attention to the
new --use-mailmap option, we started to unconditionally copy the
commit object to a temporary buffer, just in case we need the author
and committer lines updated via the mailmap mechanism, and rewrite
author and committer using the mailmap.
It turns out that this has a rather unpleasant performance
implications. In the linux kernel repository, running
$ git log --author='Junio C Hamano' --pretty=short >/dev/null
under /usr/bin/time, with and without --use-mailmap (the .mailmap
file is 118 entries long, the particular author does not appear in
it), cost (with warm cache):
[without --use-mailmap]
5.42user 0.26system 0:05.70elapsed 99%CPU (0avgtext+0avgdata 2005936maxresident)k
0inputs+0outputs (0major+137669minor)pagefaults 0swaps
[with --use-mailmap]
6.47user 0.30system 0:06.78elapsed 99%CPU (0avgtext+0avgdata 2006288maxresident)k
0inputs+0outputs (0major+137692minor)pagefaults 0swaps
which incurs about 20% overhead. The command is doing extra work,
so the extra cost may be justified.
But it is inexcusable to pay the cost when we do not need
author/committer match. In the same repository,
$ git log --grep='fix menuconfig on debian lenny' --pretty=short >/dev/null
shows very similar numbers as the above:
[without --use-mailmap]
5.32user 0.30system 0:05.63elapsed 99%CPU (0avgtext+0avgdata 2005984maxresident)k
0inputs+0outputs (0major+137672minor)pagefaults 0swaps
[with --use-mailmap]
6.64user 0.24system 0:06.89elapsed 99%CPU (0avgtext+0avgdata 2006320maxresident)k
0inputs+0outputs (0major+137694minor)pagefaults 0swaps
The latter case is an unnecessary performance regression. We may
want to _show_ the result with mailmap applied, but we do not have
to copy and rewrite the author/committer of all commits we try to
match if we do not query for these fields.
Trivially optimize this performace regression by limiting the
rewrites for only when we are matching with author/committer fields.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
////////////////////////////////////////////////////////////////
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/gittutorial.txt to get started, then see
Documentation/everyday.txt for a useful minimum set of commands, and
Documentation/git-commandname.txt for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with "man gittutorial" or "git help tutorial", and the
documentation of each command with "man git-commandname" or "git help
commandname".
CVS users may also want to read Documentation/gitcvs-migration.txt
("man gitcvs-migration" or "git help cvs-migration" if git is
installed).
Many Git online resources are accessible from http://git-scm.com/
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 (read
Documentation/SubmittingPatches for instructions on patch submission).
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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