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Many Git commands spawn git-maintenance(1) to optimize the repository in
the background. By default, performing the maintenance is for most of
the part asynchronous: we fork the executable and then continue with the
rest of our business logic.
This is working as expected for our users, but this behaviour is
somewhat problematic for our test suite as this is inherently racy. We
have many tests that verify the on-disk state of repositories, and those
tests may easily race with our background maintenance. In a similar
fashion, we may end up with processes that "leak" out of a current test
case.
Until now this tends to not be much of a problem. Our maintenance uses
git-gc(1) by default, which knows to bail out in case there aren't
either too many packfiles or too many loose objects. So even if other
data structures would need to be optimized, we won't do so unless the
object database also needs optimizations.
This is about to change though, as a subsequent commit will switch to
the "geometric" maintenance strategy as a default. The consequence is
that we will run required optimizations even if the object database is
well-optimized. And this uncovers races between our test suite and
background maintenance all over the place.
Disabling maintenance outright in our test suite is not really an
option, as it would result in significant divergence from the "real
world" and reduce our test coverage. But we've got an alternative up our
sleeves: we can ensure that garbage collection runs synchronously by
overriding the "maintenance.autoDetach" configuration.
Of course that also diverges from the real world, as we now stop testing
that background maintenance interacts in a benign way with normal Git
commands. But on the other hand this ensures that the maintenance itself
does not for example lead to data loss in a more reproducible way.
Another concern is that this would make execution of the test suite much
slower. But a quick benchmark on my machine demonstrates that this does
not seem to be the case:
Benchmark 1: meson test (revision = HEAD~)
Time (mean ± σ): 131.182 s ± 1.293 s [User: 853.737 s, System: 1160.479 s]
Range (min … max): 130.001 s … 132.563 s 3 runs
Benchmark 2: meson test (revision = HEAD)
Time (mean ± σ): 129.554 s ± 0.507 s [User: 849.040 s, System: 1152.664 s]
Range (min … max): 129.000 s … 129.994 s 3 runs
Summary
meson test (revision = HEAD) ran
1.01 ± 0.01 times faster than meson test (revision = HEAD~)
Funny enough, it even seems as if this speeds up test execution ever so
slightly, but that may just as well be noise.
Introduce a new `GIT_TEST_MAINT_AUTO_DETACH` environment variable that
allows us to override the auto-detach behaviour and set that variable in
our tests.
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.adoc to get started, then see
Documentation/giteveryday.adoc for a useful minimum set of commands, and
Documentation/git-<commandname>.adoc 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.adoc
(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).
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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