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Git's pack storage does efficient (log n) lookups in a single packfile's index, but if we have multiple packfiles, we have to linearly search each for a given object. This patch introduces some timing tests for cases where we have a large number of packs, so that we can measure any improvements we make in the following patches. The main thing we want to time is object lookup. To do this, we measure "git rev-list --objects --all", which does a fairly large number of object lookups (essentially one per object in the repository). However, we also measure the time to do a full repack, which is interesting for two reasons. One is that in addition to the usual pack lookup, it has its own linear iteration over the list of packs. And two is that because it it is the tool one uses to go from an inefficient many-pack situation back to a single pack, we care about its performance not only at marginal numbers of packs, but at the extreme cases (e.g., if you somehow end up with 5,000 packs, it is the only way to get back to 1 pack, so we need to make sure it performs well). We measure the performance of each command in three scenarios: 1 pack, 50 packs, and 1,000 packs. The 1-pack case is a baseline; any optimizations we do to handle multiple packs cannot possibly perform better than this. The 50-pack case is as far as Git should generally allow your repository to go, if you have auto-gc enabled with the default settings. So this represents the maximum performance improvement we would expect under normal circumstances. The 1,000-pack case is hopefully rare, though I have seen it in the wild where automatic maintenance was broken for some time (and the repository continued to receive pushes). This represents cases where we care less about general performance, but want to make sure that a full repack command does not take excessively long. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git - fast, scalable, distributed revision control system
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 version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from http://git-scm.com/ including full documentation and Git related tools.
See Documentation/gittutorial.txt to get started, then see
Documentation/giteveryday.txt for a useful minimum set of commands, and
Documentation/git-.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).
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://news.gmane.org/gmane.comp.version-control.git/, http://marc.info/?l=git and other archival sites.
The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.
The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (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