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ea5f220821
We add every local ref to a list so that we can mark them and all of their ancestors back to a certain cutoff point. However, if some refs point to the same commit, we will end up adding them to the list many times. Furthermore, since commit_lists are stored as linked lists, we must do an O(n) traversal of the list in order to find the right place to insert each commit. This makes building the list O(n^2) in the number of refs. For normal repositories, this isn't a big deal. We have a few hundreds refs at most, and most of them are unique. But consider an "alternates" repo that serves as an object database for many other similar repos. For reachability, it needs to keep a copy of the refs in each child repo. This means it may have a large number of refs, many of which point to the same commits. By noting commits we have already added to the list, we can shrink the size of "n" in such a repo to the number of unique commits, which is on the order of what a normal repo would contain (it's actually more than a normal repo, since child repos may have branches at different states, but in practice it tends to be much smaller than the list with duplicates). Here are the results on one particular giant repo (containing objects for all Rails forks on GitHub): $ git for-each-ref | wc -l 112514 [before] $ git fetch --no-tags ../remote.git 63.52user 0.12system 1:03.68elapsed 99%CPU (0avgtext+0avgdata 137648maxresident)k 1856inputs+48outputs (11major+19603minor)pagefaults 0swaps $ git fetch --no-tags ../remote.git 6.15user 0.08system 0:06.25elapsed 99%CPU (0avgtext+0avgdata 123856maxresident)k 0inputs+40outputs (0major+18872minor)pagefaults 0swaps Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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GIT - the stupid content tracker
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"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. 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.