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Derrick Stolee ee1f0c242e read-cache: add index.skipHash config option The previous change allowed skipping the hashing portion of the hashwrite API, using it instead as a buffered write API. Disabling the hashwrite can be particularly helpful when the write operation is in a critical path. One such critical path is the writing of the index. This operation is so critical that the sparse index was created specifically to reduce the size of the index to make these writes (and reads) faster. This trade-off between file stability at rest and write-time performance is not easy to balance. The index is an interesting case for a couple reasons: 1. Writes block users. Writing the index takes place in many user- blocking foreground operations. The speed improvement directly impacts their use. Other file formats are typically written in the background (commit-graph, multi-pack-index) or are super-critical to correctness (pack-files). 2. Index files are short lived. It is rare that a user leaves an index for a long time with many staged changes. Outside of staged changes, the index can be completely destroyed and rewritten with minimal impact to the user. Following a similar approach to one used in the microsoft/git fork [1], add a new config option (index.skipHash) that allows disabling this hashing during the index write. The cost is that we can no longer validate the contents for corruption-at-rest using the trailing hash. [1] `21fed2d914` We load this config from the repository config given by istate->repo, with a fallback to the_repository if it is not set. While older Git versions will not recognize the null hash as a special case, the file format itself is still being met in terms of its structure. Using this null hash will still allow Git operations to function across older versions. The one exception is 'git fsck' which checks the hash of the index file. This used to be a check on every index read, but was split out to just the index in `a33fc72fe9` (read-cache: force_verify_index_checksum, 2017-04-14) and released first in Git 2.13.0. Document the versions that relaxed these restrictions, with the optimistic expectation that this change will be included in Git 2.40.0. Here, we disable this check if the trailing hash is all zeroes. We add a warning to the config option that this may cause undesirable behavior with older Git versions. As a quick comparison, I tested 'git update-index --force-write' with and without index.skipHash=true on a copy of the Linux kernel repository. Benchmark 1: with hash Time (mean ± σ): 46.3 ms ± 13.8 ms [User: 34.3 ms, System: 11.9 ms] Range (min … max): 34.3 ms … 79.1 ms 82 runs Benchmark 2: without hash Time (mean ± σ): 26.0 ms ± 7.9 ms [User: 11.8 ms, System: 14.2 ms] Range (min … max): 16.3 ms … 42.0 ms 69 runs Summary 'without hash' ran 1.78 ± 0.76 times faster than 'with hash' These performance benefits are substantial enough to allow users the ability to opt-in to this feature, even with the potential confusion with older 'git fsck' versions. Test this new config option, both at a command-line level and within a submodule. The confirmation is currently limited to confirm that 'git fsck' does not complain about the index. Future updates will make this test more robust. It is critical that this test is placed before the test_index_version tests, since those tests obliterate the .git/config file and hence lose the setting from GIT_TEST_DEFAULT_HASH, if set. Signed-off-by: Derrick Stolee <derrickstolee@github.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>		2023-01-07 07:46:14 +09:00
.github	ci: use a newer `github-script` version	2022-12-10 16:32:16 +09:00
Documentation	read-cache: add index.skipHash config option	2023-01-07 07:46:14 +09:00
block-sha1	…
builtin	Merge branch 'ab/doc-synopsis-and-cmd-usage'	2022-11-29 10:41:06 +09:00
ci	Merge branch 'jx/ci-ubuntu-fix' into maint-2.38	2022-12-10 16:17:47 +09:00
compat	Merge branch 'sz/macos-fsmonitor-symlinks'	2022-11-23 11:22:25 +09:00
contrib	Merge branch 'ab/fewer-the-index-macros'	2022-12-01 18:38:07 +09:00
ewah	…
git-gui	Makefiles: change search through $(MAKEFLAGS) for GNU make 4.4	2022-12-01 07:24:12 +09:00
gitk-git	…
gitweb	…
mergetools	…
negotiator	…
oss-fuzz	…
perl	…
po	l10n: zh_TW.po: Git 2.39-rc2	2022-12-11 01:27:25 +08:00
refs	…
reftable	…
sha1collisiondetection@855827c583	…
sha1dc	…
sha256	…
t	read-cache: add index.skipHash config option	2023-01-07 07:46:14 +09:00
templates	…
trace2	…
xdiff	…
.cirrus.yml	…
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.editorconfig	…
.gitattributes	…
.gitignore	Merge branch 'ab/coccicheck-incremental'	2022-11-23 11:22:23 +09:00
.gitmodules	…
.mailmap	mailmap: update email address of Matheus Tavares	2022-12-10 09:17:36 +09:00
.tsan-suppressions	…
CODE_OF_CONDUCT.md	…
COPYING	…
GIT-VERSION-GEN	Git 2.39	2022-12-12 09:59:08 +09:00
INSTALL	…
LGPL-2.1	…
Makefile	Merge branch 'ab/coccicheck-incremental'	2022-11-23 11:22:23 +09:00
README.md	…
RelNotes	…
SECURITY.md	…
abspath.c	…
aclocal.m4	…
add-interactive.c	read-cache API & users: make discard_index() return void	2022-11-21 12:06:15 +09:00
add-interactive.h	…
add-patch.c	read-cache API & users: make discard_index() return void	2022-11-21 12:06:15 +09:00
advice.c	…
advice.h	…
alias.c	…
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alloc.c	…
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apply.h	…
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attr.c	…
attr.h	…
banned.h	…
base85.c	…
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branch.c	…
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builtin.h	…
bulk-checkin.c	…
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bundle-uri.c	…
bundle-uri.h	…
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cache-tree.c	…
cache-tree.h	…
cache.h	cocci: apply "pending" index-compatibility to some "builtin/*.c"	2022-11-21 12:06:15 +09:00
cbtree.c	…
cbtree.h	…
chdir-notify.c	…
chdir-notify.h	…
check-builtins.sh	…
checkout.c	…
checkout.h	…
chunk-format.c	…
chunk-format.h	…
color.c	…
color.h	…
column.c	…
column.h	…
combine-diff.c	…
command-list.txt	…
commit-graph.c	…
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	Merge branch 'pw/config-int-parse-fixes'	2022-11-28 12:13:43 +09:00
config.h	…
config.mak.dev	…
config.mak.in	…
config.mak.uname	…
configure.ac	…
connect.c	…
connect.h	…
connected.c	receive-pack: only use visible refs for connectivity check	2022-11-17 16:22:52 -05:00
connected.h	receive-pack: only use visible refs for connectivity check	2022-11-17 16:22:52 -05:00
convert.c	…
convert.h	…
copy.c	…
credential.c	…
credential.h	…
csum-file.c	hashfile: allow skipping the hash function	2023-01-07 07:46:14 +09:00
csum-file.h	hashfile: allow skipping the hash function	2023-01-07 07:46:14 +09:00
ctype.c	…
daemon.c	…
date.c	…
date.h	…
decorate.c	…
decorate.h	…
delta-islands.c	delta-islands: free island-related data after use	2022-11-18 18:30:49 -05:00
delta-islands.h	…
delta.h	…
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diagnose.c	…
diagnose.h	…
diff-delta.c	…
diff-lib.c	…
diff-merges.c	…
diff-merges.h	…
diff-no-index.c	…
diff.c	Merge branch 'sg/plug-line-log-leaks'	2022-11-28 12:13:46 +09:00
diff.h	…
diffcore-break.c	…
diffcore-delta.c	…
diffcore-order.c	…
diffcore-pickaxe.c	…
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editor.c	…
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environment.c	…
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fetch-negotiator.c	…
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fmt-merge-msg.c	…
fmt-merge-msg.h	…
fsck.c	…
fsck.h	…
fsmonitor--daemon.h	…
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fsmonitor-ipc.h	…
fsmonitor-path-utils.h	…
fsmonitor-settings.c	…
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fsmonitor.c	…
fsmonitor.h	…
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gettext.c	…
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git-add--interactive.perl	…
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git-bisect.sh	bisect--helper: parse subcommand with OPT_SUBCOMMAND	2022-11-11 17:04:57 -05:00
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git-curl-compat.h	…
git-cvsexportcommit.perl	…
git-cvsimport.perl	…
git-cvsserver.perl	…
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git-filter-branch.sh	…
git-instaweb.sh	…
git-merge-octopus.sh	…
git-merge-one-file.sh	…
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git-mergetool--lib.sh	…
git-mergetool.sh	…
git-p4.py	…
git-quiltimport.sh	…
git-request-pull.sh	…
git-send-email.perl	…
git-sh-i18n.sh	…
git-sh-setup.sh	…
git-submodule.sh	submodule--helper: drop "update --prefix <pfx>" for "-C <pfx> update"	2022-11-08 14:55:30 -05:00
git-svn.perl	…
git-web--browse.sh	…
git.c	Merge branch 'ab/submodule-helper-prep-only'	2022-11-23 11:22:22 +09:00
git.rc	…
gpg-interface.c	…
gpg-interface.h	…
graph.c	…
graph.h	…
grep.c	…
grep.h	…
hash-lookup.c	…
hash-lookup.h	…
hash.h	…
hashmap.c	…
hashmap.h	…
help.c	…
help.h	…
hex.c	…
hook.c	…
hook.h	…
http-backend.c	…
http-fetch.c	…
http-push.c	…
http-walker.c	…
http.c	http: redact curl h2h3 headers in info	2022-11-14 17:42:46 -05:00
http.h	…
ident.c	…
imap-send.c	…
iterator.h	…
json-writer.c	…
json-writer.h	…
khash.h	…
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kwset.h	…
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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: plug combine_filter_data leak	2022-11-21 16:43:26 +09:00
list-objects-filter.h	…
list-objects.c	…
list-objects.h	…
list.h	…
ll-merge.c	Merge branch 'rs/no-more-run-command-v'	2022-11-08 17:15:12 -05:00
ll-merge.h	…
lockfile.c	…
lockfile.h	…
log-tree.c	…
log-tree.h	…
ls-refs.c	refs: get rid of global list of hidden refs	2022-11-17 16:22:51 -05:00
ls-refs.h	…
mailinfo.c	…
mailinfo.h	…
mailmap.c	…
mailmap.h	…
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mem-pool.c	…
mem-pool.h	…
merge-blobs.c	…
merge-blobs.h	…
merge-ort-wrappers.c	…
merge-ort-wrappers.h	…
merge-ort.c	…
merge-ort.h	…
merge-recursive.c	merge-recursive: fix variable typo in error message	2022-11-27 10:26:10 +09:00
merge-recursive.h	…
merge.c	…
mergesort.h	…
midx.c	…
midx.h	…
name-hash.c	…
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notes-merge.c	…
notes-merge.h	…
notes-utils.c	…
notes-utils.h	…
notes.c	…
notes.h	…
object-file.c	object-file: use real paths when adding alternates	2022-11-25 09:44:08 +09:00
object-name.c	…
object-store.h	…
object.c	parse_object(): simplify blob conditional	2022-11-22 10:13:54 +09:00
object.h	…
oid-array.c	…
oid-array.h	…
oidmap.c	…
oidmap.h	…
oidset.c	…
oidset.h	…
oidtree.c	…
oidtree.h	…
pack-bitmap-write.c	…
pack-bitmap.c	…
pack-bitmap.h	…
pack-check.c	…
pack-mtimes.c	…
pack-mtimes.h	…
pack-objects.c	…
pack-objects.h	…
pack-revindex.c	…
pack-revindex.h	…
pack-write.c	…
pack.h	…
packfile.c	…
packfile.h	…
pager.c	…
parallel-checkout.c	…
parallel-checkout.h	…
parse-options-cb.c	…
parse-options.c	…
parse-options.h	…
patch-delta.c	…
patch-ids.c	…
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path.c	…
path.h	…
pathspec.c	…
pathspec.h	…
pkt-line.c	…
pkt-line.h	…
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-caps.c	…
protocol-caps.h	…
protocol.c	…
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	read-cache: add index.skipHash config option	2023-01-07 07:46:14 +09:00
rebase-interactive.c	…
rebase-interactive.h	…
rebase.c	…
rebase.h	…
ref-filter.c	…
ref-filter.h	…
reflog-walk.c	…
reflog-walk.h	…
reflog.c	…
reflog.h	…
refs.c	refs: get rid of global list of hidden refs	2022-11-17 16:22:51 -05:00
refs.h	refs: get rid of global list of hidden refs	2022-11-17 16:22:51 -05:00
refspec.c	…
refspec.h	…
remote-curl.c	…
remote.c	…
remote.h	…
replace-object.c	…
replace-object.h	…
repo-settings.c	Merge branch 'es/mark-gc-cruft-as-experimental'	2022-11-08 17:14:48 -05:00
repository.c	{builtin/*,repository}.c: add & use "USE_THE_INDEX_VARIABLE"	2022-11-21 12:06:15 +09:00
repository.h	Merge branch 'es/mark-gc-cruft-as-experimental'	2022-11-08 17:14:48 -05:00
rerere.c	…
rerere.h	…
reset.c	rebase: use 'skip_cache_tree_update' option	2022-11-10 21:49:34 -05:00
reset.h	…
resolve-undo.c	…
resolve-undo.h	…
revision.c	Merge branch 'ps/receive-use-only-advertised'	2022-11-23 11:22:25 +09:00
revision.h	Merge branch 'ps/receive-use-only-advertised'	2022-11-23 11:22:25 +09:00
run-command.c	Merge branch 'rs/no-more-run-command-v'	2022-11-08 17:15:12 -05:00
run-command.h	Merge branch 'rs/no-more-run-command-v'	2022-11-08 17:15:12 -05:00
scalar.c	Merge branch 'js/remove-stale-scalar-repos'	2022-11-23 11:22:23 +09:00
send-pack.c	…
send-pack.h	…
sequencer.c	rebase --update-refs: avoid unintended ref deletion	2022-12-09 19:31:45 +09:00
sequencer.h	sequencer: stop exporting GIT_REFLOG_ACTION	2022-11-09 18:15:43 -05:00
serve.c	…
serve.h	…
server-info.c	…
setup.c	…
sh-i18n--envsubst.c	…
sha1dc_git.c	…
sha1dc_git.h	Makefile & test-tool: replace "DC_SHA1" variable with a "define"	2022-11-07 22:11:51 -05:00
shallow.c	…
shallow.h	…
shared.mak	Merge branch 'ab/gnumake-4.4-fix'	2022-12-01 18:38:07 +09:00
shell.c	…
shortlog.h	…
sideband.c	…
sideband.h	…
sigchain.c	…
sigchain.h	…
simple-ipc.h	…
sparse-index.c	…
sparse-index.h	…
split-index.c	…
split-index.h	…
stable-qsort.c	…
strbuf.c	…
strbuf.h	…
streaming.c	…
streaming.h	…
string-list.c	…
string-list.h	…
strmap.c	…
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strvec.c	…
strvec.h	…
sub-process.c	…
sub-process.h	…
submodule-config.c	…
submodule-config.h	…
submodule.c	Merge branch 'jt/submodule-on-demand'	2022-11-23 11:22:25 +09:00
submodule.h	submodule API & "absorbgitdirs": remove "----recursive" option	2022-11-08 14:55:30 -05:00
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	…
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trailer.h	…
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transport-internal.h	…
transport.c	…
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	…
unix-stream-server.c	…
unix-stream-server.h	…
unpack-trees.c	unpack-trees: add 'skip_cache_tree_update' option	2022-11-10 21:49:34 -05:00
unpack-trees.h	unpack-trees: add 'skip_cache_tree_update' option	2022-11-10 21:49:34 -05:00
upload-pack.c	refs: get rid of global list of hidden refs	2022-11-17 16:22:51 -05:00
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url.c	…
url.h	…
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urlmatch.h	…
usage.c	…
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userdiff.h	…
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wrap-for-bin.sh	…
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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 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