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Neeraj Singh c0f4752ed2 core.fsyncmethod: batched disk flushes for loose-objects
When adding many objects to a repo with `core.fsync=loose-object`,
the cost of fsync'ing each object file can become prohibitive.

One major source of the cost of fsync is the implied flush of the
hardware writeback cache within the disk drive. This commit introduces
a new `core.fsyncMethod=batch` option that batches up hardware flushes.
It hooks into the bulk-checkin odb-transaction functionality, takes
advantage of tmp-objdir, and uses the writeout-only support code.

When the new mode is enabled, we do the following for each new object:
1a. Create the object in a tmp-objdir.
2a. Issue a pagecache writeback request and wait for it to complete.

At the end of the entire transaction when unplugging bulk checkin:
1b. Issue an fsync against a dummy file to flush the log and hardware
   writeback cache, which should by now have seen the tmp-objdir writes.
2b. Rename all of the tmp-objdir files to their final names.
3b. When updating the index and/or refs, we assume that Git will issue
   another fsync internal to that operation. This is not the default
   today, but the user now has the option of syncing the index and there
   is a separate patch series to implement syncing of refs.

On a filesystem with a singular journal that is updated during name
operations (e.g. create, link, rename, etc), such as NTFS, HFS+, or XFS
we would expect the fsync to trigger a journal writeout so that this
sequence is enough to ensure that the user's data is durable by the time
the git command returns. This sequence also ensures that no object files
appear in the main object store unless they are fsync-durable.

Batch mode is only enabled if core.fsync includes loose-objects. If
the legacy core.fsyncObjectFiles setting is enabled, but core.fsync does
not include loose-objects, we will use file-by-file fsyncing.

In step (1a) of the sequence, the tmp-objdir is created lazily to avoid
work if no loose objects are ever added to the ODB. We use a tmp-objdir
to maintain the invariant that no loose-objects are visible in the main
ODB unless they are properly fsync-durable. This is important since
future ODB operations that try to create an object with specific
contents will silently drop the new data if an object with the target
hash exists without checking that the loose-object contents match the
hash. Only a full git-fsck would restore the ODB to a functional state
where dataloss doesn't occur.

In step (1b) of the sequence, we issue a fsync against a dummy file
created specifically for the purpose. This method has a little higher
cost than using one of the input object files, but makes adding new
callers of this mechanism easier, since we don't need to figure out
which object file is "last" or risk sharing violations by caching the fd
of the last object file.

_Performance numbers_:

Linux - Hyper-V VM running Kernel 5.11 (Ubuntu 20.04) on a fast SSD.
Mac - macOS 11.5.1 running on a Mac mini on a 1TB Apple SSD.
Windows - Same host as Linux, a preview version of Windows 11.

Adding 500 files to the repo with 'git add' Times reported in seconds.

object file syncing | Linux | Mac   | Windows
--------------------|-------|-------|--------
           disabled | 0.06  |  0.35 | 0.61
              fsync | 1.88  | 11.18 | 2.47
              batch | 0.15  |  0.41 | 1.53

Signed-off-by: Neeraj Singh <neerajsi@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-04-06 13:13:01 -07:00
.github
Documentation core.fsyncmethod: batched disk flushes for loose-objects 2022-04-06 13:13:01 -07:00
block-sha1
builtin bulk-checkin: rebrand plug/unplug APIs as 'odb transactions' 2022-04-06 13:02:09 -07:00
ci compat: auto-detect if zlib has uncompress2() 2022-01-26 09:05:55 -08:00
compat core.fsyncmethod: add writeout-only mode 2022-03-10 15:10:22 -08:00
contrib Merge branch 'ns/core-fsyncmethod' into ns/batch-fsync 2022-04-06 13:01:54 -07:00
ewah
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gitk-git
gitweb
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po l10n: Update Catalan translation 2022-01-23 09:40:52 +01:00
ppc
refs Merge branch 'ps/avoid-unnecessary-hook-invocation-with-packed-refs' 2022-02-18 13:53:27 -08:00
reftable reftable: rename writer_stats to reftable_writer_stats 2022-02-23 13:36:26 -08:00
sha1collisiondetection@855827c583
sha1dc
sha256
t Merge branch 'ps/fetch-atomic-fixup' 2022-03-13 22:56:17 +00:00
templates Makefile: add "$(QUIET)" boilerplate to shared.mak 2022-03-03 14:14:55 -08:00
trace2 trace2: use designated initializers for "struct tr2_dst" 2022-02-24 15:58:55 -08:00
xdiff xdiff: handle allocation failure when merging 2022-02-16 10:58:16 -08:00
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COPYING
GIT-VERSION-GEN Git 2.35.1 2022-01-28 16:48:42 -08:00
INSTALL
LGPL-2.1
Makefile Merge branch 'ns/core-fsyncmethod' into ns/batch-fsync 2022-04-06 13:01:54 -07:00
README.md Merge branch 'po/readme-mention-contributor-hints' 2022-02-09 14:20:59 -08:00
RelNotes Name the next one 2.36 to prepare for 2.35.1 2022-01-28 16:57:10 -08:00
SECURITY.md
abspath.c
aclocal.m4
add-interactive.c diff.[ch]: have diff_free() call clear_pathspec(opts.pathspec) 2022-02-16 13:50:13 -08:00
add-interactive.h
add-patch.c Merge branch 'pw/add-p-hunk-split-fix' 2022-02-09 14:20:59 -08:00
advice.c switch: mention the --detach option when dying due to lack of a branch 2022-02-25 22:21:48 -08:00
advice.h switch: mention the --detach option when dying due to lack of a branch 2022-02-25 22:21:48 -08:00
alias.c
alias.h
alloc.c
alloc.h
apply.c range-diff: plug memory leak in common invocation 2022-03-04 13:24:19 -08:00
apply.h range-diff: plug memory leak in common invocation 2022-03-04 13:24:19 -08:00
archive-tar.c archive-*.c: use designated initializers for "struct archiver" 2022-02-24 15:59:20 -08:00
archive-zip.c Merge branch 'ab/c99-designated-initializers' 2022-03-06 21:25:32 -08:00
archive.c i18n: remove from i18n strings that do not hold translatable parts 2022-02-04 13:58:28 -08:00
archive.h
attr.c
attr.h
banned.h C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code 2022-02-21 19:14:19 -08:00
base85.c
bisect.c
bisect.h
blame.c Merge branch 'ab/diff-free-more' 2022-02-25 15:47:36 -08:00
blame.h
blob.c
blob.h
bloom.c
bloom.h
branch.c Merge branch 'gc/branch-recurse-submodules' 2022-02-18 13:53:29 -08:00
branch.h branch: add --recurse-submodules option for branch creation 2022-02-04 08:16:39 -08:00
builtin.h
bulk-checkin.c core.fsyncmethod: batched disk flushes for loose-objects 2022-04-06 13:13:01 -07:00
bulk-checkin.h core.fsyncmethod: batched disk flushes for loose-objects 2022-04-06 13:13:01 -07:00
bundle.c
bundle.h
cache-tree.c
cache-tree.h
cache.h core.fsyncmethod: batched disk flushes for loose-objects 2022-04-06 13:13:01 -07:00
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 Merge branch 'ns/core-fsyncmethod' into ns/batch-fsync 2022-04-06 13:01:54 -07:00
commit-graph.h commit-graph: fix memory leak in misused string_list API 2022-03-04 13:24:18 -08:00
commit-reach.c
commit-reach.h
commit-slab-decl.h
commit-slab-impl.h
commit-slab.h
commit.c Merge branch 'ab/config-based-hooks-2' 2022-02-09 14:21:00 -08:00
commit.h
common-main.c
config.c core.fsyncmethod: batched disk flushes for loose-objects 2022-04-06 13:13:01 -07:00
config.h Merge branch 'ds/sparse-checkout-requires-per-worktree-config' 2022-02-25 15:47:33 -08:00
config.mak.dev
config.mak.in
config.mak.uname Merge branch 'ns/core-fsyncmethod' into ns/batch-fsync 2022-04-06 13:01:54 -07:00
configure.ac configure.ac: fix HAVE_SYNC_FILE_RANGE definition 2022-04-06 09:36:19 -07:00
connect.c ls-remote & transport API: release "struct transport_ls_refs_options" 2022-02-06 18:02:34 -08:00
connect.h
connected.c
connected.h
convert.c convert.c: use designated initializers for "struct stream_filter*" 2022-02-24 15:59:43 -08:00
convert.h
copy.c
credential.c urlmatch.c: add and use a *_release() function 2022-03-04 13:24:18 -08:00
credential.h
csum-file.c core.fsync: introduce granular fsync control infrastructure 2022-03-10 15:10:22 -08:00
csum-file.h core.fsync: introduce granular fsync control infrastructure 2022-03-10 15:10:22 -08:00
ctype.c
daemon.c
date.c date API: add and use a date_mode_release() 2022-02-16 09:40:00 -08:00
date.h date API: add and use a date_mode_release() 2022-02-16 09:40:00 -08:00
decorate.c
decorate.h
delta-islands.c
delta-islands.h
delta.h
detect-compiler
diff-delta.c
diff-lib.c
diff-merges.c Merge branch 'ja/i18n-common-messages' 2022-02-25 15:47:35 -08:00
diff-merges.h
diff-no-index.c
diff.c Merge branch 'ab/plug-random-leaks' 2022-03-13 22:56:18 +00:00
diff.h Merge branch 'js/diff-filter-negation-fix' 2022-02-16 15:14:30 -08:00
diffcore-break.c
diffcore-delta.c
diffcore-order.c
diffcore-pickaxe.c
diffcore-rename.c
diffcore-rotate.c
diffcore.h
dir-iterator.c
dir-iterator.h
dir.c dir: force untracked cache with core.untrackedCache 2022-02-17 14:47:13 -08:00
dir.h
editor.c
entry.c
entry.h
environment.c Merge branch 'ns/core-fsyncmethod' into ns/batch-fsync 2022-04-06 13:01:54 -07:00
environment.h
exec-cmd.c
exec-cmd.h
fetch-negotiator.c repo-settings: rename the traditional default fetch.negotiationAlgorithm 2022-02-02 09:36:17 -08:00
fetch-negotiator.h
fetch-pack.c Merge branch 'ps/fetch-optim-with-commit-graph' 2022-02-23 16:58:03 -08:00
fetch-pack.h
fmt-merge-msg.c
fmt-merge-msg.h
fsck.c
fsck.h
fsmonitor.c
fsmonitor.h
fuzz-commit-graph.c
fuzz-pack-headers.c
fuzz-pack-idx.c
generate-cmdlist.sh
generate-configlist.sh
generate-hooklist.sh
gettext.c
gettext.h
git-add--interactive.perl
git-archimport.perl
git-bisect.sh
git-compat-util.h Merge branch 'ns/core-fsyncmethod' into ns/batch-fsync 2022-04-06 13:01:54 -07:00
git-curl-compat.h
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 'ab/config-based-hooks-2' 2022-02-09 14:21:00 -08:00
git-quiltimport.sh
git-request-pull.sh
git-send-email.perl
git-sh-i18n.sh
git-sh-setup.sh git-sh-setup: remove remnant bits referring to `git-legacy-stash` 2022-01-27 18:00:09 -08:00
git-submodule.sh clone, submodule: pass partial clone filters to submodules 2022-02-09 15:38:36 -08:00
git-svn.perl
git-web--browse.sh
git.c Merge branch 'ab/grep-patterntype' 2022-02-25 15:47:36 -08:00
git.rc
gpg-interface.c Merge branch 'fs/gpgsm-update' 2022-03-13 22:56:17 +00:00
gpg-interface.h
graph.c log: fix memory leak if --graph is passed multiple times 2022-02-11 10:06:40 -08:00
graph.h log: fix memory leak if --graph is passed multiple times 2022-02-11 10:06:40 -08:00
grep.c Merge branch 'rs/pcre-invalid-utf8-fix-fix' 2022-02-25 15:47:38 -08:00
grep.h grep: simplify config parsing and option parsing 2022-02-15 18:00:50 -08:00
hash-lookup.c
hash-lookup.h
hash.h
hashmap.c
hashmap.h
help.c help: don't print "\n" before single-section output 2022-02-23 13:41:37 -08:00
help.h help: add --no-[external-commands|aliases] for use with --all 2022-02-23 13:41:37 -08:00
hex.c
hook.c
hook.h
http-backend.c date API: create a date.h, split from cache.h 2022-02-16 09:40:00 -08:00
http-fetch.c
http-push.c
http-walker.c
http.c
http.h
ident.c date API: create a date.h, split from cache.h 2022-02-16 09:40:00 -08:00
imap-send.c imap-send.c: use designated initializers for "struct imap_server_conf" 2022-02-24 15:57:56 -08:00
iterator.h
json-writer.c
json-writer.h
khash.h
kwset.c
kwset.h
levenshtein.c
levenshtein.h
line-log.c
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: make callers responsible for showing warnings 2022-02-02 10:02:27 -08:00
ll-merge.h ll-merge: make callers responsible for showing warnings 2022-02-02 10:02:27 -08:00
lockfile.c
lockfile.h
log-tree.c show, log: include conflict/warning messages in --remerge-diff headers 2022-02-02 10:02:28 -08:00
log-tree.h
ls-refs.c i18n: factorize "invalid value" messages 2022-02-04 13:58:28 -08:00
ls-refs.h
mailinfo.c
mailinfo.h
mailmap.c
mailmap.h
match-trees.c
mem-pool.c mem-pool: don't assume uintmax_t is aligned enough for all types 2022-01-24 10:26:40 -08:00
mem-pool.h
merge-blobs.c ll-merge: make callers responsible for showing warnings 2022-02-02 10:02:27 -08:00
merge-blobs.h
merge-ort-wrappers.c
merge-ort-wrappers.h
merge-ort.c Merge branch 'en/merge-ort-align-verbosity-with-recursive' 2022-03-13 22:56:17 +00:00
merge-ort.h show, log: include conflict/warning messages in --remerge-diff headers 2022-02-02 10:02:28 -08:00
merge-recursive.c merge-ort: format messages slightly different for use in headers 2022-02-02 10:02:27 -08:00
merge-recursive.h merge-ort: format messages slightly different for use in headers 2022-02-02 10:02:27 -08:00
merge.c
mergesort.c
mergesort.h
midx.c core.fsync: introduce granular fsync control infrastructure 2022-03-10 15:10:22 -08:00
midx.h midx: read `RIDX` chunk when present 2022-01-27 12:07:53 -08:00
name-hash.c
notes-cache.c
notes-cache.h
notes-merge.c Merge branch 'ab/diff-free-more' 2022-02-25 15:47:36 -08:00
notes-merge.h
notes-utils.c
notes-utils.h
notes.c
notes.h
object-file.c core.fsyncmethod: batched disk flushes for loose-objects 2022-04-06 13:13:01 -07:00
object-name.c Merge branch 'ab/date-mode-release' 2022-02-25 15:47:36 -08:00
object-store.h
object.c
object.h
oid-array.c
oid-array.h
oidmap.c
oidmap.h
oidset.c
oidset.h
oidtree.c
oidtree.h
pack-bitmap-write.c core.fsync: introduce granular fsync control infrastructure 2022-03-10 15:10:22 -08:00
pack-bitmap.c pack-bitmap.c: gracefully fallback after opening pack/MIDX 2022-01-27 12:07:53 -08:00
pack-bitmap.h
pack-check.c
pack-objects.c
pack-objects.h
pack-revindex.c midx: read `RIDX` chunk when present 2022-01-27 12:07:53 -08:00
pack-revindex.h
pack-write.c core.fsync: introduce granular fsync control infrastructure 2022-03-10 15:10:22 -08:00
pack.h
packfile.c
packfile.h
pager.c
parallel-checkout.c i18n: factorize "invalid value" messages 2022-02-04 13:58:28 -08:00
parallel-checkout.h
parse-options-cb.c
parse-options.c Merge branch 'ja/i18n-common-messages' 2022-02-25 15:47:35 -08:00
parse-options.h Merge branch 'ja/i18n-common-messages' 2022-02-25 15:47:35 -08:00
patch-delta.c
patch-ids.c
patch-ids.h
path.c
path.h repository.c: free the "path cache" in repo_clear() 2022-03-04 13:24:19 -08:00
pathspec.c
pathspec.h
pkt-line.c
pkt-line.h
preload-index.c
pretty.c
pretty.h date API: create a date.h, split from cache.h 2022-02-16 09:40:00 -08:00
prio-queue.c
prio-queue.h
progress.c progress API: unify stop_progress{,_msg}(), fix trace2 bug 2022-02-03 15:39:59 -08:00
progress.h progress API: unify stop_progress{,_msg}(), fix trace2 bug 2022-02-03 15:39:59 -08:00
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: plug memory leak in read_patches() 2022-03-04 13:24:19 -08:00
range-diff.h
reachable.c
reachable.h
read-cache.c core.fsync: new option to harden the index 2022-03-10 15:10:22 -08:00
rebase-interactive.c
rebase-interactive.h
rebase.c
rebase.h
ref-filter.c date API: add and use a date_mode_release() 2022-02-16 09:40:00 -08:00
ref-filter.h
reflog-walk.c
reflog-walk.h date API: create a date.h, split from cache.h 2022-02-16 09:40:00 -08:00
refs.c Merge branch 'ps/fetch-atomic' 2022-03-13 22:56:16 +00:00
refs.h Merge branch 'ps/fetch-atomic' 2022-03-13 22:56:16 +00:00
refspec.c refspec.c: use designated initializers for "struct refspec_item" 2022-02-24 15:59:53 -08:00
refspec.h
remote-curl.c remote-curl.c: free memory in cmd_main() 2022-03-04 13:24:18 -08:00
remote.c refs API: remove "failure_errno" from refs_resolve_ref_unsafe() 2022-01-26 15:58:41 -08:00
remote.h
replace-object.c
replace-object.h
repo-settings.c Merge branch 'en/fetch-negotiation-default-fix' 2022-02-16 15:14:30 -08:00
repository.c Merge branch 'ab/plug-random-leaks' 2022-03-13 22:56:18 +00:00
repository.h repository.c: free the "path cache" in repo_clear() 2022-03-04 13:24:19 -08:00
rerere.c ll-merge: make callers responsible for showing warnings 2022-02-02 10:02:27 -08:00
rerere.h
reset.c Merge branch 'pw/use-in-process-checkout-in-rebase' 2022-02-18 13:53:27 -08:00
reset.h rebase --apply: set ORIG_HEAD correctly 2022-01-26 12:08:53 -08:00
resolve-undo.c
resolve-undo.h
revision.c Merge branch 'ab/grep-patterntype' 2022-02-25 15:47:36 -08:00
revision.h Merge branch 'ah/log-no-graph' 2022-02-23 16:58:03 -08:00
run-command.c Merge branch 'ab/config-based-hooks-2' 2022-02-09 14:21:00 -08:00
run-command.h
send-pack.c
send-pack.h
sequencer.c Merge branch 'ja/i18n-common-messages' 2022-02-25 15:47:35 -08:00
sequencer.h create_autostash(): remove unneeded parameter 2022-01-26 12:08:53 -08:00
serve.c
serve.h
server-info.c
setup.c i18n: factorize "invalid value" messages 2022-02-04 13:58:28 -08:00
sh-i18n--envsubst.c
sha1dc_git.c
sha1dc_git.h
shallow.c
shallow.h
shared.mak Makefiles: add and use wildcard "mkdir -p" template 2022-03-03 14:14:55 -08:00
shell.c
shortlog.h
sideband.c
sideband.h
sigchain.c
sigchain.h
simple-ipc.h
sparse-index.c Merge branch 'en/present-despite-skipped' 2022-03-09 13:38:23 -08:00
sparse-index.h
split-index.c split-index: it really is incompatible with the sparse index 2022-01-23 17:06:23 -08:00
split-index.h
stable-qsort.c
strbuf.c date API: create a date.h, split from cache.h 2022-02-16 09:40:00 -08:00
strbuf.h
streaming.c
streaming.h
string-list.c
string-list.h
strmap.c
strmap.h
strvec.c
strvec.h
sub-process.c
sub-process.h
submodule-config.c Merge branch 'ja/i18n-common-messages' 2022-02-25 15:47:35 -08:00
submodule-config.h branch: add --recurse-submodules option for branch creation 2022-02-04 08:16:39 -08:00
submodule.c branch: add --recurse-submodules option for branch creation 2022-02-04 08:16:39 -08:00
submodule.h branch: add --recurse-submodules option for branch creation 2022-02-04 08:16:39 -08:00
symlinks.c
tag.c
tag.h
tar.h
tempfile.c
tempfile.h
thread-utils.c
thread-utils.h
tmp-objdir.c log: clean unneeded objects during `log --remerge-diff` 2022-02-02 10:02:27 -08:00
tmp-objdir.h log: clean unneeded objects during `log --remerge-diff` 2022-02-02 10:02:27 -08:00
trace.c C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code 2022-02-21 19:14:19 -08:00
trace.h C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code 2022-02-21 19:14:19 -08:00
trace2.c C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code 2022-02-21 19:14:19 -08:00
trace2.h C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code 2022-02-21 19:14:19 -08:00
trailer.c
trailer.h
transport-helper.c
transport-internal.h
transport.c transport: stop needlessly copying bundle header references 2022-03-04 13:24:18 -08:00
transport.h ls-remote & transport API: release "struct transport_ls_refs_options" 2022-02-06 18:02:34 -08:00
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.h
upload-pack.c
upload-pack.h
url.c
url.h
urlmatch.c urlmatch.c: add and use a *_release() function 2022-03-04 13:24:18 -08:00
urlmatch.h urlmatch.c: add and use a *_release() function 2022-03-04 13:24:18 -08:00
usage.c C99: remove hardcoded-out !HAVE_VARIADIC_MACROS code 2022-02-21 19:14:19 -08:00
userdiff.c userdiff.c: use designated initializers for "struct userdiff_driver" 2022-02-24 15:59:27 -08:00
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 Merge branch 'ds/sparse-checkout-requires-per-worktree-config' 2022-02-25 15:47:33 -08:00
worktree.h worktree: create init_worktree_config() 2022-02-08 09:49:20 -08:00
wrap-for-bin.sh
wrapper.c core.fsyncmethod: add writeout-only mode 2022-03-10 15:10:22 -08:00
write-or-die.c core.fsync: introduce granular fsync control infrastructure 2022-03-10 15:10:22 -08:00
ws.c
wt-status.c
wt-status.h
xdiff-interface.c
xdiff-interface.h
zlib.c

README.md

Build status

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