76d7602631
Git uses zlib for its own object store, but calls gzip when creating tgz
archives. Add an option to perform the gzip compression for the latter
using zlib, without depending on the external gzip binary.
Plug it in by making write_block a function pointer and switching to a
compressing variant if the filter command has the magic value "git
archive gzip". Does that indirection slow down tar creation? Not
really, at least not in this test:
$ hyperfine -w3 -L rev HEAD,origin/main -p 'git checkout {rev} && make' \
'./git -C ../linux archive --format=tar HEAD # {rev}'
Benchmark #1: ./git -C ../linux archive --format=tar HEAD # HEAD
Time (mean ± σ): 4.044 s ± 0.007 s [User: 3.901 s, System: 0.137 s]
Range (min … max): 4.038 s … 4.059 s 10 runs
Benchmark #2: ./git -C ../linux archive --format=tar HEAD # origin/main
Time (mean ± σ): 4.047 s ± 0.009 s [User: 3.903 s, System: 0.138 s]
Range (min … max): 4.038 s … 4.066 s 10 runs
How does tgz creation perform?
$ hyperfine -w3 -L command 'gzip -cn','git archive gzip' \
'./git -c tar.tgz.command="{command}" -C ../linux archive --format=tgz HEAD'
Benchmark #1: ./git -c tar.tgz.command="gzip -cn" -C ../linux archive --format=tgz HEAD
Time (mean ± σ): 20.404 s ± 0.006 s [User: 23.943 s, System: 0.401 s]
Range (min … max): 20.395 s … 20.414 s 10 runs
Benchmark #2: ./git -c tar.tgz.command="git archive gzip" -C ../linux archive --format=tgz HEAD
Time (mean ± σ): 23.807 s ± 0.023 s [User: 23.655 s, System: 0.145 s]
Range (min … max): 23.782 s … 23.857 s 10 runs
Summary
'./git -c tar.tgz.command="gzip -cn" -C ../linux archive --format=tgz HEAD' ran
1.17 ± 0.00 times faster than './git -c tar.tgz.command="git archive gzip" -C ../linux archive --format=tgz HEAD'
So the internal implementation takes 17% longer on the Linux repo, but
uses 2% less CPU time. That's because the external gzip can run in
parallel on its own processor, while the internal one works sequentially
and avoids the inter-process communication overhead.
What are the benefits? Only an internal sequential implementation can
offer this eco mode, and it allows avoiding the gzip(1) requirement.
This implementation uses the helper functions from our zlib.c instead of
the convenient gz* functions from zlib, because the latter doesn't give
the control over the generated gzip header that the next patch requires.
Original-patch-by: Rohit Ashiwal <rohit.ashiwal265@gmail.com>
Signed-off-by: René Scharfe <l.s.r@web.de>
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