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Patrick Steinhardt 6754159767 refs: implement reference transaction hook The low-level reference transactions used to update references are currently completely opaque to the user. While certainly desirable in most usecases, there are some which might want to hook into the transaction to observe all queued reference updates as well as observing the abortion or commit of a prepared transaction. One such usecase would be to have a set of replicas of a given Git repository, where we perform Git operations on all of the repositories at once and expect the outcome to be the same in all of them. While there exist hooks already for a certain subset of Git commands that could be used to implement a voting mechanism for this, many others currently don't have any mechanism for this. The above scenario is the motivation for the new "reference-transaction" hook that reaches directly into Git's reference transaction mechanism. The hook receives as parameter the current state the transaction was moved to ("prepared", "committed" or "aborted") and gets via its standard input all queued reference updates. While the exit code gets ignored in the "committed" and "aborted" states, a non-zero exit code in the "prepared" state will cause the transaction to be aborted prematurely. Given the usecase described above, a voting mechanism can now be implemented via this hook: as soon as it gets called, it will take all of stdin and use it to cast a vote to a central service. When all replicas of the repository agree, the hook will exit with zero, otherwise it will abort the transaction by returning non-zero. The most important upside is that this will catch _all_ commands writing references at once, allowing to implement strong consistency for reference updates via a single mechanism. In order to test the impact on the case where we don't have any "reference-transaction" hook installed in the repository, this commit introduce two new performance tests for git-update-refs(1). Run against an empty repository, it produces the following results: Test origin/master HEAD -------------------------------------------------------------------- 1400.2: update-ref 2.70(2.10+0.71) 2.71(2.10+0.73) +0.4% 1400.3: update-ref --stdin 0.21(0.09+0.11) 0.21(0.07+0.14) +0.0% The performance test p1400.2 creates, updates and deletes a branch a thousand times, thus averaging runtime of git-update-refs over 3000 invocations. p1400.3 instead calls `git-update-refs --stdin` three times and queues a thousand creations, updates and deletes respectively. As expected, p1400.3 consistently shows no noticeable impact, as for each batch of updates there's a single call to access(3P) for the negative hook lookup. On the other hand, for p1400.2, one can see an impact caused by this patchset. But doing five runs of the performance tests where each one was run with GIT_PERF_REPEAT_COUNT=10, the overhead ranged from -1.5% to +1.1%. These inconsistent performance numbers can be explained by the overhead of spawning 3000 processes. This shows that the overhead of assembling the hook path and executing access(3P) once to check if it's there is mostly outweighed by the operating system's overhead. Signed-off-by: Patrick Steinhardt <ps@pks.im> Signed-off-by: Junio C Hamano <gitster@pobox.com>		2020-06-19 10:46:13 -07:00
.github	Merge branch 'es/advertise-contribution-doc'	2020-06-17 21:54:06 -07:00
Documentation	refs: implement reference transaction hook	2020-06-19 10:46:13 -07:00
block-sha1	…
builtin	Merge branch 'en/sparse-checkout'	2020-06-17 21:54:02 -07:00
ci	Merge branch 'jk/ci-only-on-selected-branches'	2020-05-29 15:12:19 -07:00
compat	Merge branch 'js/msvc-build-fix'	2020-06-17 21:54:03 -07:00
contrib	Merge branch 'vs/complete-stash-show-p-fix'	2020-06-08 18:06:29 -07:00
ewah	…
git-gui	Merge https://github.com/prati0100/git-gui	2020-05-21 11:15:04 -07:00
gitk-git	…
gitweb	…
mergetools	…
negotiator	…
perl	…
po	Merge branch 'master' of github.com:ruester/git-po-de	2020-05-30 11:26:53 +08:00
ppc	…
refs	refs: improve documentation for ref iterator	2020-05-20 10:39:02 -07:00
sha1collisiondetection@855827c583	…
sha1dc	…
sha256	…
t	refs: implement reference transaction hook	2020-06-19 10:46:13 -07:00
templates	…
trace2	…
vcs-svn	…
xdiff	…
.cirrus.yml	…
.clang-format	…
.editorconfig	…
.gitattributes	…
.gitignore	…
.gitmodules	…
.mailmap	…
.travis.yml	…
.tsan-suppressions	…
CODE_OF_CONDUCT.md	…
COPYING	…
GIT-VERSION-GEN	The third batch	2020-06-17 21:54:06 -07:00
INSTALL	…
LGPL-2.1	…
Makefile	Merge branch 'lo/sparse-universal-zero-init'	2020-06-02 13:35:04 -07:00
README.md	…
RelNotes	Start the post 2.27 cycle	2020-06-02 13:35:05 -07:00
abspath.c	…
aclocal.m4	…
add-interactive.c	…
add-interactive.h	…
add-patch.c	Merge branch 'js/checkout-p-new-file'	2020-06-08 18:06:31 -07:00
advice.c	…
advice.h	…
alias.c	…
alias.h	…
alloc.c	…
alloc.h	…
apply.c	…
apply.h	…
archive-tar.c	…
archive-zip.c	…
archive.c	…
archive.h	…
argv-array.c	…
argv-array.h	…
attr.c	…
attr.h	…
banned.h	…
base85.c	…
bisect.c	…
bisect.h	…
blame.c	…
blame.h	…
blob.c	…
blob.h	…
bloom.c	Merge branch 'ds/line-log-on-bloom'	2020-06-08 18:06:26 -07:00
bloom.h	Merge branch 'ds/line-log-on-bloom'	2020-06-08 18:06:26 -07:00
branch.c	…
branch.h	…
bugreport.c	…
builtin.h	…
bulk-checkin.c	…
bulk-checkin.h	…
bundle.c	…
bundle.h	…
cache-tree.c	…
cache-tree.h	…
cache.h	…
chdir-notify.c	…
chdir-notify.h	…
check-builtins.sh	…
check_bindir	…
checkout.c	…
checkout.h	…
color.c	…
color.h	…
column.c	…
column.h	…
combine-diff.c	…
command-list.txt	Merge branch 'bc/faq'	2020-05-24 19:39:36 -07:00
commit-graph.c	Merge branch 'tb/commit-graph-no-check-oids'	2020-06-08 18:06:27 -07:00
commit-graph.h	…
commit-reach.c	…
commit-reach.h	…
commit-slab-decl.h	…
commit-slab-impl.h	…
commit-slab.h	…
commit.c	…
commit.h	…
common-main.c	…
config.c	…
config.h	…
config.mak.dev	…
config.mak.in	…
config.mak.uname	Merge branch 'cb/no-more-gmtime'	2020-05-20 08:33:27 -07:00
configure.ac	…
connect.c	stateless-connect: send response end packet	2020-05-24 16:26:00 -07:00
connect.h	stateless-connect: send response end packet	2020-05-24 16:26:00 -07:00
connected.c	…
connected.h	…
convert.c	…
convert.h	…
copy.c	…
credential-cache--daemon.c	…
credential-cache.c	…
credential-store.c	…
credential.c	…
credential.h	…
csum-file.c	…
csum-file.h	…
ctype.c	…
daemon.c	…
date.c	…
decorate.c	…
decorate.h	…
delta-islands.c	…
delta-islands.h	…
delta.h	…
detect-compiler	…
diff-delta.c	…
diff-lib.c	…
diff-no-index.c	…
diff.c	Merge branch 'jk/diff-memuse-optim-with-stat-unmatch'	2020-06-17 21:54:00 -07:00
diff.h	…
diffcore-break.c	…
diffcore-delta.c	…
diffcore-order.c	…
diffcore-pickaxe.c	…
diffcore-rename.c	…
diffcore.h	…
dir-iterator.c	…
dir-iterator.h	…
dir.c	Merge branch 'en/do-match-pathspec-fix'	2020-06-17 21:54:03 -07:00
dir.h	…
editor.c	…
entry.c	…
environment.c	…
exec-cmd.c	…
exec-cmd.h	…
fast-import.c	Merge branch 'en/fast-import-looser-date'	2020-06-02 13:35:05 -07:00
fetch-negotiator.c	…
fetch-negotiator.h	…
fetch-pack.c	stateless-connect: send response end packet	2020-05-24 16:26:00 -07:00
fetch-pack.h	…
fmt-merge-msg.c	…
fmt-merge-msg.h	…
fsck.c	Merge branch 'rs/fsck-duplicate-names-in-trees'	2020-06-08 18:06:29 -07:00
fsck.h	…
fsmonitor.c	…
fsmonitor.h	…
fuzz-commit-graph.c	fuzz-commit-graph: properly free graph struct	2020-06-08 10:02:29 -07:00
fuzz-pack-headers.c	…
fuzz-pack-idx.c	…
generate-cmdlist.sh	…
generate-configlist.sh	…
gettext.c	…
gettext.h	…
git-add--interactive.perl	checkout -p: handle new files correctly	2020-05-27 14:50:20 -07:00
git-archimport.perl	…
git-bisect.sh	bisect: avoid tailing CR characters from revision in replay	2020-05-20 10:13:19 -07:00
git-compat-util.h	Merge branch 'cb/no-more-gmtime'	2020-05-20 08:33:27 -07:00
git-cvsexportcommit.perl	…
git-cvsimport.perl	…
git-cvsserver.perl	…
git-difftool--helper.sh	…
git-filter-branch.sh	…
git-instaweb.sh	…
git-merge-octopus.sh	…
git-merge-one-file.sh	…
git-merge-resolve.sh	…
git-mergetool--lib.sh	…
git-mergetool.sh	…
git-p4.py	Merge branch 'bk/p4-prepare-p4-only-fix'	2020-06-02 13:35:01 -07:00
git-parse-remote.sh	…
git-quiltimport.sh	…
git-rebase--preserve-merges.sh	…
git-request-pull.sh	…
git-send-email.perl	…
git-sh-i18n.sh	…
git-sh-setup.sh	…
git-submodule.sh	…
git-svn.perl	…
git-web--browse.sh	…
git.c	…
git.rc	…
gpg-interface.c	…
gpg-interface.h	…
graph.c	…
graph.h	…
grep.c	…
grep.h	…
hash.h	…
hashmap.c	…
hashmap.h	…
help.c	…
help.h	…
hex.c	…
http-backend.c	…
http-fetch.c	…
http-push.c	…
http-walker.c	…
http.c	…
http.h	…
ident.c	…
imap-send.c	…
interdiff.c	…
interdiff.h	…
iterator.h	…
json-writer.c	…
json-writer.h	…
khash.h	…
kwset.c	…
kwset.h	…
levenshtein.c	…
levenshtein.h	…
line-log.c	Merge branch 'ds/line-log-on-bloom'	2020-06-08 18:06:26 -07:00
line-log.h	…
line-range.c	…
line-range.h	…
linear-assignment.c	…
linear-assignment.h	…
list-objects-filter-options.c	…
list-objects-filter-options.h	…
list-objects-filter.c	…
list-objects-filter.h	…
list-objects.c	…
list-objects.h	…
list.h	…
ll-merge.c	…
ll-merge.h	…
lockfile.c	…
lockfile.h	…
log-tree.c	…
log-tree.h	…
ls-refs.c	…
ls-refs.h	…
mailinfo.c	…
mailinfo.h	…
mailmap.c	…
mailmap.h	…
match-trees.c	…
mem-pool.c	…
mem-pool.h	…
merge-blobs.c	…
merge-blobs.h	…
merge-recursive.c	…
merge-recursive.h	…
merge.c	…
mergesort.c	…
mergesort.h	…
midx.c	…
midx.h	…
name-hash.c	…
notes-cache.c	…
notes-cache.h	…
notes-merge.c	…
notes-merge.h	…
notes-utils.c	…
notes-utils.h	…
notes.c	…
notes.h	…
object-store.h	…
object.c	…
object.h	…
oid-array.c	…
oid-array.h	…
oidmap.c	…
oidmap.h	…
oidset.c	…
oidset.h	…
pack-bitmap-write.c	…
pack-bitmap.c	…
pack-bitmap.h	…
pack-check.c	…
pack-objects.c	…
pack-objects.h	…
pack-revindex.c	…
pack-revindex.h	…
pack-write.c	…
pack.h	…
packfile.c	…
packfile.h	…
pager.c	…
parse-options-cb.c	…
parse-options.c	…
parse-options.h	…
patch-delta.c	…
patch-ids.c	…
patch-ids.h	…
path.c	…
path.h	…
pathspec.c	…
pathspec.h	…
pkt-line.c	pkt-line: define PACKET_READ_RESPONSE_END	2020-05-24 16:26:00 -07:00
pkt-line.h	pkt-line: define PACKET_READ_RESPONSE_END	2020-05-24 16:26:00 -07:00
preload-index.c	…
pretty.c	…
pretty.h	…
prio-queue.c	…
prio-queue.h	…
progress.c	…
progress.h	…
promisor-remote.c	…
promisor-remote.h	…
prompt.c	…
prompt.h	…
protocol.c	config: let feature.experimental imply protocol.version=2	2020-05-21 09:31:42 -07:00
protocol.h	…
prune-packed.c	…
prune-packed.h	…
quote.c	…
quote.h	…
range-diff.c	…
range-diff.h	…
reachable.c	…
reachable.h	…
read-cache.c	…
rebase-interactive.c	…
rebase-interactive.h	…
rebase.c	…
rebase.h	…
ref-filter.c	…
ref-filter.h	…
reflog-walk.c	…
reflog-walk.h	…
refs.c	refs: implement reference transaction hook	2020-06-19 10:46:13 -07:00
refs.h	refs.h: clarify reflog iteration order	2020-05-20 10:39:01 -07:00
refspec.c	…
refspec.h	…
remote-curl.c	stateless-connect: send response end packet	2020-05-24 16:26:00 -07:00
remote-testsvn.c	…
remote.c	…
remote.h	stateless-connect: send response end packet	2020-05-24 16:26:00 -07:00
replace-object.c	…
replace-object.h	…
repo-settings.c	…
repository.c	…
repository.h	…
rerere.c	…
rerere.h	…
reset.c	…
reset.h	…
resolve-undo.c	…
resolve-undo.h	…
revision.c	Merge branch 'ds/line-log-on-bloom'	2020-06-08 18:06:26 -07:00
revision.h	…
run-command.c	…
run-command.h	…
send-pack.c	…
send-pack.h	…
sequencer.c	…
sequencer.h	…
serve.c	pkt-line: define PACKET_READ_RESPONSE_END	2020-05-24 16:26:00 -07:00
serve.h	…
server-info.c	…
setup.c	…
sh-i18n--envsubst.c	…
sha1-file.c	…
sha1-lookup.c	…
sha1-lookup.h	…
sha1-name.c	…
sha1dc_git.c	…
sha1dc_git.h	…
shallow.c	…
shallow.h	…
shell.c	…
shortlog.h	…
sideband.c	…
sideband.h	…
sigchain.c	…
sigchain.h	…
split-index.c	…
split-index.h	…
stable-qsort.c	…
strbuf.c	…
strbuf.h	…
streaming.c	…
streaming.h	…
string-list.c	…
string-list.h	…
sub-process.c	…
sub-process.h	…
submodule-config.c	…
submodule-config.h	…
submodule.c	…
submodule.h	…
symlinks.c	…
tag.c	…
tag.h	…
tar.h	…
tempfile.c	…
tempfile.h	…
thread-utils.c	…
thread-utils.h	…
tmp-objdir.c	…
tmp-objdir.h	…
trace.c	…
trace.h	…
trace2.c	…
trace2.h	…
trailer.c	…
trailer.h	…
transport-helper.c	…
transport-internal.h	…
transport.c	stateless-connect: send response end packet	2020-05-24 16:26:00 -07:00
transport.h	…
tree-diff.c	…
tree-walk.c	…
tree-walk.h	…
tree.c	…
tree.h	…
unicode-width.h	…
unimplemented.sh	…
unix-socket.c	…
unix-socket.h	…
unpack-trees.c	Merge branch 'en/sparse-checkout'	2020-05-20 08:33:29 -07:00
unpack-trees.h	…
upload-pack.c	upload-pack: use upload_pack_data fields in receive_needs()	2020-05-18 12:58:02 -07:00
upload-pack.h	…
url.c	…
url.h	…
urlmatch.c	…
urlmatch.h	…
usage.c	…
userdiff.c	…
userdiff.h	…
utf8.c	…
utf8.h	…
varint.c	…
varint.h	…
version.c	…
version.h	…
versioncmp.c	…
walker.c	…
walker.h	…
wildmatch.c	…
wildmatch.h	…
worktree.c	…
worktree.h	…
wrap-for-bin.sh	…
wrapper.c	…
write-or-die.c	…
ws.c	…
wt-status.c	…
wt-status.h	…
xdiff-interface.c	…
xdiff-interface.h	…
zlib.c	…

README.md

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). 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 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