mirror of
https://github.com/git/git.git
synced 2026-01-12 13:53:11 +09:00
8e55634b47
When fetching from a remote repository we will by default write what has
been fetched into the special FETCH_HEAD reference. The order in which
references are written depends on whether the reference is for merge or
not, which, despite some other conditions, is also determined based on
whether the old object ID the reference is being updated from actually
exists in the repository.
To write FETCH_HEAD we thus loop through all references thrice: once for
the references that are about to be merged, once for the references that
are not for merge, and finally for all references that are ignored. For
every iteration, we then look up the old object ID to determine whether
the referenced object exists so that we can label it as "not-for-merge"
if it doesn't exist. It goes without saying that this can be expensive
in case where we are fetching a lot of references.
While this is hard to avoid in the case where we're writing FETCH_HEAD,
users can in fact ask us to skip this work via `--no-write-fetch-head`.
In that case, we do not care for the result of those lookups at all
because we don't have to order writes to FETCH_HEAD in the first place.
Skip this busywork in case we're not writing to FETCH_HEAD. The
following benchmark performs a mirror-fetch in a repository with about
two million references via `git fetch --prune --no-write-fetch-head
+refs/*:refs/*`:
Benchmark 1: HEAD~
Time (mean ± σ): 75.388 s ± 1.942 s [User: 71.103 s, System: 8.953 s]
Range (min … max): 73.184 s … 76.845 s 3 runs
Benchmark 2: HEAD
Time (mean ± σ): 69.486 s ± 1.016 s [User: 65.941 s, System: 8.806 s]
Range (min … max): 68.864 s … 70.659 s 3 runs
Summary
'HEAD' ran
1.08 ± 0.03 times faster than 'HEAD~'
Signed-off-by: Patrick Steinhardt <ps@pks.im>
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 https://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-<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).
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 and Documentation/CodingGuidelines).
Those wishing to help with error message, usage and informational message
string translations (localization l10) should see po/README.md
(a po file is a Portable Object file that holds the translations).
To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org (not the Git list). The mailing list archives are available at https://lore.kernel.org/git/, http://marc.info/?l=git and other archival sites.
Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.
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