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Patrick Steinhardt 8e55634b47 fetch: avoid lookup of commits when not appending to FETCH_HEAD 
When fetching from a remote repository we will by default write what has
been fetched into the special FETCH_HEAD reference. The order in which
references are written depends on whether the reference is for merge or
not, which, despite some other conditions, is also determined based on
whether the old object ID the reference is being updated from actually
exists in the repository.

To write FETCH_HEAD we thus loop through all references thrice: once for
the references that are about to be merged, once for the references that
are not for merge, and finally for all references that are ignored. For
every iteration, we then look up the old object ID to determine whether
the referenced object exists so that we can label it as "not-for-merge"
if it doesn't exist. It goes without saying that this can be expensive
in case where we are fetching a lot of references.

While this is hard to avoid in the case where we're writing FETCH_HEAD,
users can in fact ask us to skip this work via `--no-write-fetch-head`.
In that case, we do not care for the result of those lookups at all
because we don't have to order writes to FETCH_HEAD in the first place.

Skip this busywork in case we're not writing to FETCH_HEAD. The
following benchmark performs a mirror-fetch in a repository with about
two million references via `git fetch --prune --no-write-fetch-head
+refs/*:refs/*`:

    Benchmark 1: HEAD~
      Time (mean ± σ):     75.388 s ±  1.942 s    [User: 71.103 s, System: 8.953 s]
      Range (min … max):   73.184 s … 76.845 s    3 runs

    Benchmark 2: HEAD
      Time (mean ± σ):     69.486 s ±  1.016 s    [User: 65.941 s, System: 8.806 s]
      Range (min … max):   68.864 s … 70.659 s    3 runs

    Summary
      'HEAD' ran
        1.08 ± 0.03 times faster than 'HEAD~'

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-03-01 10:13:46 -08:00
..
add.c add: remove support for git-legacy-stash 2022-01-27 18:00:15 -08:00
am.c Merge branch 'ab/config-based-hooks-2' 2022-02-09 14:21:00 -08:00
annotate.c strvec: rename struct fields 2020-07-30 19:18:06 -07:00
apply.c
archive.c use xopen() to handle fatal open(2) failures 2021-08-25 14:39:08 -07:00
bisect--helper.c bisect--helper: add space between colon and following sentence 2021-10-01 15:47:53 -07:00
blame.c Merge branch 'ld/sparse-diff-blame' 2021-12-21 15:03:17 -08:00
branch.c Merge branch 'gc/branch-recurse-submodules' 2022-02-18 13:53:29 -08:00
bugreport.c hook-list.h: add a generated list of hooks, like config-list.h 2021-09-27 09:44:54 -07:00
bundle.c Merge branch 'ab/bundle-remove-verbose-option' 2021-10-03 21:49:20 -07:00
cat-file.c cat-file: s/_/-/ in typo'd usage_msg_optf() message 2022-01-12 10:12:39 -08:00
check-attr.c cache.h: flip NO_THE_INDEX_COMPATIBILITY_MACROS switch 2019-01-24 11:55:06 -08:00
check-ignore.c dir.[ch]: replace dir_init() with DIR_INIT 2021-07-01 12:32:22 -07:00
check-mailmap.c shortlog: remove unused(?) "repo-abbrev" feature 2021-01-12 14:04:42 -08:00
check-ref-format.c
checkout--worker.c pkt-line.[ch]: remove unused packet_read_line_buf() 2021-10-15 13:09:40 -07:00
checkout-index.c checkout-index: integrate with sparse index 2022-01-13 13:49:45 -08:00
checkout.c Merge branch 'js/short-help-outside-repo-fix' 2022-02-18 13:53:30 -08:00
clean.c Merge branch 'vd/sparse-clean-etc' 2022-02-17 16:25:05 -08:00
clone.c Merge branch 'ab/release-transport-ls-refs-options' 2022-02-18 13:53:29 -08:00
column.c column: fix parsing of the '--nl' option 2021-08-26 14:36:27 -07:00
commit-graph.c Merge branch 'ab/ignore-replace-while-working-on-commit-graph' 2021-11-01 13:48:08 -07:00
commit-tree.c use xopen() to handle fatal open(2) failures 2021-08-25 14:39:08 -07:00
commit.c i18n: turn even more messages into "cannot be used together" ones 2022-01-05 13:31:00 -08:00
config.c urlmatch.[ch]: add and use URLMATCH_CONFIG_INIT 2021-10-01 14:22:51 -07:00
count-objects.c
credential-cache--daemon.c unix-socket: add backlog size option to unix_stream_listen() 2021-03-15 14:32:51 -07:00
credential-cache.c credential-cache: check for windows specific errors 2021-09-14 09:30:54 -07:00
credential-store.c Use a better name for the function interpolating paths 2021-07-26 12:17:16 -07:00
credential.c doc: fix git credential synopsis 2021-10-28 09:57:09 -07:00
describe.c i18n: turn even more messages into "cannot be used together" ones 2022-01-05 13:31:00 -08:00
diff-files.c Merge branch 'jc/diffcore-rotate' 2021-02-25 16:43:30 -08:00
diff-index.c diff-index: restore -c/--cc options handling 2021-09-07 11:11:35 -07:00
diff-tree.c i18n: refactor "foo and bar are mutually exclusive" 2022-01-05 13:29:23 -08:00
diff.c builtin/diff.c: fix "git-diff" usage string typo 2022-02-02 11:30:53 -08:00
difftool.c i18n: turn "options are incompatible" into "cannot be used together" 2022-01-05 13:29:23 -08:00
env--helper.c assert PARSE_OPT_NONEG in parse-options callbacks 2020-09-30 12:53:47 -07:00
fast-export.c Merge branch 'ja/i18n-similar-messages' 2022-01-10 11:52:56 -08:00
fast-import.c usage.c API users: use die_message() for "fatal :" + exit 128 2021-12-07 13:25:15 -08:00
fetch-pack.c connect, transport: encapsulate arg in struct 2021-02-05 13:49:54 -08:00
fetch.c fetch: avoid lookup of commits when not appending to FETCH_HEAD 2022-03-01 10:13:46 -08:00
fmt-merge-msg.c merge: allow to pretend a merge is made into a different branch 2021-12-20 14:55:02 -08:00
for-each-ref.c for-each-ref: delay parsing of --sort=<atom> options 2021-10-20 14:33:07 -07:00
for-each-repo.c builtin/for-each-repo: remove unnecessary argv copy to plug leak 2021-07-26 12:19:20 -07:00
fsck.c run-command API users: use strvec_pushl(), not argv construction 2021-11-25 22:15:07 -08:00
gc.c Merge branch 'ab/config-based-hooks-2' 2022-02-09 14:21:00 -08:00
get-tar-commit-id.c builtin/get-tar-commit-id: make hash size independent 2019-04-01 11:57:39 +09:00
grep.c grep: fix a "path_list" memory leak 2021-10-23 10:45:25 -07:00
hash-object.c hash-object: fix a trivial leak in --path 2022-02-06 17:55:55 -08:00
help.c run-command API users: use strvec_pushl(), not argv construction 2021-11-25 22:15:07 -08:00
hook.c git hook run: add an --ignore-missing flag 2022-01-07 15:19:34 -08:00
index-pack.c i18n: factorize "--foo requires --bar" and the like 2022-01-05 13:31:00 -08:00
init-db.c i18n: refactor "foo and bar are mutually exclusive" 2022-01-05 13:29:23 -08:00
interpret-trailers.c Use OPT_CALLBACK and OPT_CALLBACK_F 2020-04-28 10:47:10 -07:00
log.c Merge branch 'en/remerge-diff' 2022-02-16 15:14:29 -08:00
ls-files.c Merge branch 'ja/i18n-similar-messages' 2022-01-10 11:52:56 -08:00
ls-remote.c ls-remote & transport API: release "struct transport_ls_refs_options" 2022-02-06 18:02:34 -08:00
ls-tree.c tree.h API: simplify read_tree_recursive() signature 2021-03-20 16:09:26 -07:00
mailinfo.c mailinfo: allow squelching quoted CRLF warning 2021-05-10 15:06:22 +09:00
mailsplit.c use xopen() to handle fatal open(2) failures 2021-08-25 14:39:08 -07:00
merge-base.c rebase: --fork-point regression fix 2020-02-11 09:59:39 -08:00
merge-file.c xdiff: implement a zealous diff3, or "zdiff3" 2021-12-01 14:45:58 -08:00
merge-index.c merge-index: ensure full index 2021-04-14 13:47:21 -07:00
merge-ours.c builtins + test helpers: use return instead of exit() in cmd_* 2021-06-09 09:15:58 +09:00
merge-recursive.c Ensure index matches head before invoking merge machinery, round N 2019-08-19 10:08:03 -07:00
merge-tree.c xdiff users: use designated initializers for out_line 2021-05-11 12:47:31 +09:00
merge.c Merge branch 'pw/use-in-process-checkout-in-rebase' 2022-02-18 13:53:27 -08:00
mktag.c fsck: report invalid object type-path combinations 2021-10-01 15:06:01 -07:00
mktree.c builtins + test helpers: use return instead of exit() in cmd_* 2021-06-09 09:15:58 +09:00
multi-pack-index.c builtin/multi-pack-index.c: don't leak concatenated options 2021-10-28 15:32:14 -07:00
mv.c mv: refuse to move sparse paths 2021-09-28 10:31:02 -07:00
name-rev.c name-rev.c: use strbuf_getline instead of limited size buffer 2022-01-10 09:39:26 -08:00
notes.c Merge branch 'ab/usage-die-message' 2022-01-10 11:52:53 -08:00
pack-objects.c checkout/fetch/pull/pack-objects: allow -h outside a repository 2022-02-08 09:54:44 -08:00
pack-redundant.c builtin/pack-redundant: avoid casting buffers to struct object_id 2021-04-27 16:31:38 +09:00
pack-refs.c Honor core.precomposeUnicode in more places 2019-04-26 10:54:03 +09:00
patch-id.c patch-id: fix scan_hunk_header on diffs with 1 line of before/after 2022-02-02 11:24:23 -08:00
prune-packed.c Lib-ify prune-packed 2020-03-24 15:04:44 -07:00
prune.c Merge branch 'ns/tmp-objdir' 2022-01-03 16:24:15 -08:00
pull.c Merge branch 'js/short-help-outside-repo-fix' 2022-02-18 13:53:30 -08:00
push.c i18n: turn "options are incompatible" into "cannot be used together" 2022-01-05 13:29:23 -08:00
range-diff.c column, range-diff: downcase option description 2021-03-29 14:06:08 -07:00
read-tree.c Change unpack_trees' 'reset' flag into an enum 2021-09-27 13:38:37 -07:00
rebase.c Merge branch 'pw/use-in-process-checkout-in-rebase' 2022-02-18 13:53:27 -08:00
receive-pack.c Merge branch 'cb/clear-quarantine-early-on-all-ref-update-errors' 2022-02-18 13:53:27 -08:00
reflog.c builtin/reflog.c: use parse-options api for expire, delete subcommands 2022-01-10 14:13:06 -08:00
remote-ext.c strvec: convert builtin/ callers away from argv_array name 2020-07-28 15:02:18 -07:00
remote-fd.c
remote.c Merge branch 'ab/designated-initializers-more' 2021-10-18 15:47:57 -07:00
repack.c Merge branch 'ja/i18n-similar-messages' 2022-01-10 11:52:56 -08:00
replace.c run-command API users: use strvec_pushl(), not argv construction 2021-11-25 22:15:07 -08:00
rerere.c xdiff users: use designated initializers for out_line 2021-05-11 12:47:31 +09:00
reset.c Merge branch 'vd/sparse-clean-etc' 2022-02-17 16:25:05 -08:00
rev-list.c i18n: turn even more messages into "cannot be used together" ones 2022-01-05 13:31:00 -08:00
rev-parse.c refs: drop "broken" flag from for_each_fullref_in() 2021-09-27 12:36:45 -07:00
revert.c Merge branch 'ds/mergies-with-sparse-index' 2021-09-20 15:20:45 -07:00
rm.c Merge branch 'ja/i18n-similar-messages' 2022-01-10 11:52:56 -08:00
send-pack.c Merge branch 'jk/http-push-status-fix' 2021-10-29 15:43:12 -07:00
shortlog.c parse-options.[ch]: consistently use "enum parse_opt_result" 2021-10-08 14:13:11 -07:00
show-branch.c i18n: turn "options are incompatible" into "cannot be used together" 2022-01-05 13:29:23 -08:00
show-index.c builtin/show-index: set the algorithm for object IDs 2021-04-27 16:31:39 +09:00
show-ref.c refs: switch peel_ref() to peel_iterated_oid() 2021-01-21 15:51:31 -08:00
sparse-checkout.c Merge branch 'en/sparse-checkout-leakfix' 2022-02-11 16:56:01 -08:00
stash.c Merge branch 'js/no-more-legacy-stash' 2022-02-16 15:14:30 -08:00
stripspace.c stripspace: allow -s/-c outside git repository 2018-12-26 15:41:47 -08:00
submodule--helper.c Merge branch 'gc/branch-recurse-submodules' 2022-02-18 13:53:29 -08:00
symbolic-ref.c symbolic-ref: don't leak shortened refname in check_symref() 2021-03-14 15:57:59 -07:00
tag.c i18n: tag.c factorize i18n strings 2022-01-05 13:31:00 -08:00
unpack-file.c
unpack-objects.c hash: provide per-algorithm null OIDs 2021-04-27 16:31:39 +09:00
update-index.c Merge branch 'vd/sparse-clean-etc' 2022-02-17 16:25:05 -08:00
update-ref.c update-ref: fix streaming of status updates 2021-09-03 11:35:15 -07:00
update-server-info.c
upload-archive.c upload-archive: use regular "struct child_process" pattern 2021-11-25 22:15:07 -08:00
upload-pack.c upload-pack: document and rename --advertise-refs 2021-08-05 08:59:37 -07:00
var.c var: add GIT_DEFAULT_BRANCH variable 2021-11-03 13:25:36 -07:00
verify-commit.c Merge branch 'jk/no-system-includes-in-dot-c' 2019-07-31 14:38:56 -07:00
verify-pack.c Merge branch 'bc/sha-256-part-3' 2020-08-11 18:04:11 -07:00
verify-tag.c verify-tag: drop signal.h include 2019-06-19 08:19:21 -07:00
worktree.c Merge branch 'ab/config-based-hooks-2' 2022-02-09 14:21:00 -08:00
write-tree.c cmd_{read,write}_tree: rename "unused" variable that is used 2019-05-13 14:22:53 +09:00