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Kevin Willford b3dfeebb92 rebase: avoid computing unnecessary patch IDs 
The `rebase` family of Git commands avoid applying patches that were
already integrated upstream. They do that by using the revision walking
option that computes the patch IDs of the two sides of the rebase
(local-only patches vs upstream-only ones) and skipping those local
patches whose patch ID matches one of the upstream ones.

In many cases, this causes unnecessary churn, as already the set of
paths touched by a given commit would suffice to determine that an
upstream patch has no local equivalent.

This hurts performance in particular when there are a lot of upstream
patches, and/or large ones.

Therefore, let's introduce the concept of a "diff-header-only" patch ID,
compare those first, and only evaluate the "full" patch ID lazily.

Please note that in contrast to the "full" patch IDs, those
"diff-header-only" patch IDs are prone to collide with one another, as
adjacent commits frequently touch the very same files. Hence we now
have to be careful to allow multiple hash entries with the same hash.
We accomplish that by using the hashmap_add() function that does not even
test for hash collisions.  This also allows us to evaluate the full patch ID
lazily, i.e. only when we found commits with matching diff-header-only
patch IDs.

We add a performance test that demonstrates ~1-6% improvement.  In
practice this will depend on various factors such as how many upstream
changes and how big those changes are along with whether file system
caches are cold or warm.  As Git's test suite has no way of catching
performance regressions, we also add a regression test that verifies
that the full patch ID computation is skipped when the diff-header-only
computation suffices.

Signed-off-by: Kevin Willford <kcwillford@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-08-11 14:39:16 -07:00
..
add.c Merge branch 'jc/add-u-A-default-to-top' into maint 2015-11-05 12:18:12 -08:00
am.c builtin/am.c: use error_errno() 2016-05-09 12:29:08 -07:00
annotate.c
apply.c Merge branch 'rs/apply-name-terminate' 2016-06-03 14:38:04 -07:00
archive.c
bisect--helper.c
blame.c Merge branch 'tb/blame-force-read-cache-to-workaround-safe-crlf' 2016-04-13 14:12:41 -07:00
branch.c Merge branch 'nd/worktree-various-heads' 2016-05-23 14:54:29 -07:00
bundle.c
cat-file.c Merge branch 'jk/cat-file-buffered-batch-all' 2016-05-31 12:40:54 -07:00
check-attr.c give "nbuf" strbuf a more meaningful name 2016-02-01 13:43:02 -08:00
check-ignore.c give "nbuf" strbuf a more meaningful name 2016-02-01 13:43:02 -08:00
check-mailmap.c strbuf: introduce strbuf_getline_{lf,nul}() 2016-01-15 10:12:51 -08:00
check-ref-format.c use xmallocz to avoid size arithmetic 2016-02-22 14:51:09 -08:00
checkout-index.c checkout-index: disallow "--no-stage" option 2016-02-01 13:43:49 -08:00
checkout.c Merge branch 'nd/worktree-various-heads' 2016-05-23 14:54:29 -07:00
clean.c Merge branch 'jk/tighten-alloc' 2016-02-26 13:37:16 -08:00
clone.c Merge branch 'sb/clone-shallow-passthru' 2016-05-06 14:45:43 -07:00
column.c column: read lines with strbuf_getline() 2016-01-15 10:35:07 -08:00
commit-tree.c Merge branch 'jc/commit-tree-ignore-commit-gpgsign' 2016-05-13 13:18:27 -07:00
commit.c Merge branch 'pb/commit-verbose-config' 2016-05-23 14:54:32 -07:00
config.c Merge branch 'jk/config-get-urlmatch' into maint 2016-04-14 18:57:43 -07:00
count-objects.c prepare_packed_git(): refactor garbage reporting in pack directory 2015-08-17 09:14:59 -07:00
credential.c
describe.c Remove get_object_hash. 2015-11-20 08:02:05 -05:00
diff-files.c diff: run arguments through precompose_argv 2016-05-13 14:35:49 -07:00
diff-index.c diff: run arguments through precompose_argv 2016-05-13 14:35:49 -07:00
diff-tree.c Merge branch 'ar/diff-args-osx-precompose' 2016-05-23 14:54:35 -07:00
diff.c Merge branch 'ar/diff-args-osx-precompose' 2016-05-23 14:54:35 -07:00
fast-export.c convert trivial cases to ALLOC_ARRAY 2016-02-22 14:51:09 -08:00
fetch-pack.c fetch-pack: fix object_id of exact sha1 2016-03-01 11:19:19 -08:00
fetch.c Merge branch 'nd/error-errno' 2016-05-17 14:38:28 -07:00
fmt-merge-msg.c Merge branch 'rs/pop-commit' into maint 2015-12-11 11:14:13 -08:00
for-each-ref.c ref-filter: add option to match literal pattern 2015-09-17 10:02:49 -07:00
fsck.c fsck_head_link(): remove unneeded flag variable 2016-04-10 11:35:33 -07:00
gc.c Merge branch 'dk/gc-idx-wo-pack' into maint 2015-12-04 11:33:08 -08:00
get-tar-commit-id.c usage: do not insist that standard input must come from a file 2015-10-16 15:27:52 -07:00
grep.c Merge branch 'bc/object-id' 2016-05-06 14:45:44 -07:00
hash-object.c Merge branch 'jk/options-cleanup' 2016-02-10 14:20:08 -08:00
help.c builtin/help.c: use warning_errno() 2016-05-09 12:29:08 -07:00
index-pack.c Merge branch 'va/i18n-misc-updates' 2016-05-17 14:38:23 -07:00
init-db.c Merge branch 'jk/check-repository-format' 2016-04-13 14:12:28 -07:00
interpret-trailers.c interpret-trailers: add option for in-place editing 2016-01-14 12:22:17 -08:00
log.c rebase: avoid computing unnecessary patch IDs 2016-08-11 14:39:16 -07:00
ls-files.c Merge branch 'jk/options-cleanup' 2016-02-10 14:20:08 -08:00
ls-remote.c ls-remote: add support for showing symrefs 2016-01-19 10:07:56 -08:00
ls-tree.c convert trivial sprintf / strcpy calls to xsnprintf 2015-09-25 10:18:18 -07:00
mailinfo.c mailinfo: libify 2015-10-21 15:59:34 -07:00
mailsplit.c builtin/mailsplit.c: use error_errno() 2016-05-09 12:29:08 -07:00
merge-base.c convert trivial cases to ALLOC_ARRAY 2016-02-22 14:51:09 -08:00
merge-file.c builtin/merge-file.c: use error_errno() 2016-05-09 12:29:08 -07:00
merge-index.c use sha1_to_hex_r() instead of strcpy 2015-10-05 11:08:05 -07:00
merge-ours.c
merge-recursive.c convert trivial sprintf / strcpy calls to xsnprintf 2015-09-25 10:18:18 -07:00
merge-tree.c struct name_entry: use struct object_id instead of unsigned char sha1[20] 2016-04-25 14:23:42 -07:00
merge.c Merge branch 'en/merge-trivial-fix' 2016-04-25 15:17:15 -07:00
mktag.c usage: do not insist that standard input must come from a file 2015-10-16 15:27:52 -07:00
mktree.c Merge branch 'jk/tighten-alloc' 2016-02-26 13:37:16 -08:00
mv.c Merge branch 'sb/mv-submodule-fix' 2016-04-29 12:59:07 -07:00
name-rev.c Merge branch 'js/name-rev-use-oldest-ref' 2016-05-03 14:08:13 -07:00
notes.c worktree.c: make find_shared_symref() return struct worktree * 2016-04-22 14:09:37 -07:00
pack-objects.c Merge branch 'nd/error-errno' 2016-05-17 14:38:28 -07:00
pack-redundant.c convert trivial cases to ALLOC_ARRAY 2016-02-22 14:51:09 -08:00
pack-refs.c
patch-id.c Merge branch 'rs/patch-id-use-skip-prefix' 2016-06-03 14:38:03 -07:00
prune-packed.c
prune.c Merge branch 'jk/repository-extension' into maint 2015-11-03 15:32:25 -08:00
pull.c Merge branch 'va/i18n-misc-updates' 2016-05-17 14:38:23 -07:00
push.c Merge branch 'mm/push-default-warning' 2016-02-26 13:37:25 -08:00
read-tree.c convert trivial sprintf / strcpy calls to xsnprintf 2015-09-25 10:18:18 -07:00
receive-pack.c Merge branch 'dt/pre-refs-backend' 2016-04-25 15:17:15 -07:00
reflog.c struct name_entry: use struct object_id instead of unsigned char sha1[20] 2016-04-25 14:23:42 -07:00
remote-ext.c typofix: assorted typofixes in comments, documentation and messages 2016-05-06 13:16:37 -07:00
remote-fd.c
remote.c i18n: remote: add comment for translators 2016-05-09 12:20:40 -07:00
repack.c strbuf: introduce strbuf_getline_{lf,nul}() 2016-01-15 10:12:51 -08:00
replace.c Merge branch 'js/replace-edit-use-editor-configuration' 2016-04-29 12:59:07 -07:00
rerere.c Sync with 2.6.1 2015-10-05 13:20:08 -07:00
reset.c Remove get_object_hash. 2015-11-20 08:02:05 -05:00
rev-list.c Merge branch 'maint-2.4' into maint-2.5 2016-03-17 11:24:14 -07:00
rev-parse.c Merge branch 'jk/rev-parse-local-env-vars' into maint 2016-04-14 18:57:44 -07:00
revert.c
rm.c Merge branch 'nd/error-errno' 2016-05-17 14:38:28 -07:00
send-pack.c Merge branch 'sk/send-pack-all-fix' 2016-04-13 14:12:33 -07:00
shortlog.c Merge branch 'jk/shortlog' 2016-01-28 16:10:14 -08:00
show-branch.c Merge branch 'rs/show-branch-argv-array' into maint 2015-12-11 11:14:14 -08:00
show-ref.c show-ref: stop using PARSE_OPT_NO_INTERNAL_HELP 2015-11-20 08:02:07 -05:00
stripspace.c stripspace: call U+0020 a "space" instead of a "blank" 2016-01-29 16:02:34 -08:00
submodule--helper.c submodule: remove bashism from shell script 2016-06-01 11:32:53 -07:00
symbolic-ref.c symbolic-ref: propagate error code from create_symref() 2015-12-21 12:03:03 -08:00
tag.c Merge branch 'st/verify-tag' 2016-04-29 12:59:09 -07:00
unpack-file.c convert trivial sprintf / strcpy calls to xsnprintf 2015-09-25 10:18:18 -07:00
unpack-objects.c Remove get_object_hash. 2015-11-20 08:02:05 -05:00
update-index.c builtin/update-index.c: prefer "err" to "errno" in process_lstat_error 2016-05-09 12:29:08 -07:00
update-ref.c tag, update-ref: improve description of option "create-reflog" 2015-09-11 09:50:02 -07:00
update-server-info.c
upload-archive.c builtin/upload-archive.c: use error_errno() 2016-05-09 12:29:08 -07:00
var.c
verify-commit.c
verify-pack.c
verify-tag.c verify-tag: move tag verification code to tag.c 2016-04-22 14:06:46 -07:00
worktree.c Merge branch 'nd/worktree-various-heads' 2016-05-23 14:54:29 -07:00
write-tree.c