bisect: avoid copying ancestor list for non-merge commits
During a bisection, hg needs to compute a list of all ancestors for every
candidate commit. This is accomplished via a bottom-up traversal of the set of
candidates, during which each revision's ancestor list is populated using the
ancestor list of its parent(s). Previously, this involved copying the entire
list, which could be very long in if the bisection range was large.
To help improve this, we can observe that each candidate commit is visited
exactly once, at which point its ancestor list is copied into its children's
lists and then dropped. In the case of non-merge commits, a commit's ancestor
list consists exactly of its parent's list plus itself. This means that we can
trivially reuse the parent's existing list for one of its non-merge children,
which avoids copying entirely if that commit is the parent's only child. This
makes bisections over linear ranges of commits much faster.
During some informal testing in the large publicly-available `mozilla-central`
repository, this noticeably sped up bisections over large ranges of history:
Setup:
$ cd mozilla-central
$ hg bisect --reset
$ hg bisect --good 0
$ hg log -r tip -T '{rev}\n'
628417
Test:
$ time hg bisect --bad tip --noupdate
Before:
real 3m35.927s
user 3m35.553s
sys 0m0.319s
After:
real 1m41.142s
user 1m40.810s
sys 0m0.285s
#testcases abortcommand abortflag
#if abortflag
$ cat >> $HGRCPATH <<EOF
> [alias]
> abort = histedit --abort
> EOF
#endif
$ . "$TESTDIR/histedit-helpers.sh"
Enable extension used by this test
$ cat >>$HGRCPATH <<EOF
> [extensions]
> histedit=
> EOF
=================================
Test backup-bundle config option|
=================================
Repo setup:
$ hg init foo
$ cd foo
$ echo first>file
$ hg ci -qAm one
$ echo second>>file
$ hg ci -m two
$ echo third>>file
$ hg ci -m three
$ echo forth>>file
$ hg ci -m four
$ hg log -G --style compact
@ 3[tip] 7d5187087c79 1970-01-01 00:00 +0000 test
| four
|
o 2 80d23dfa866d 1970-01-01 00:00 +0000 test
| three
|
o 1 6153eb23e623 1970-01-01 00:00 +0000 test
| two
|
o 0 36b4bdd91f5b 1970-01-01 00:00 +0000 test
one
Test when `backup-bundle` config option is enabled:
$ hg histedit -r '36b4bdd91f5b' --commands - << EOF
> pick 36b4bdd91f5b 0 one
> pick 6153eb23e623 1 two
> roll 80d23dfa866d 2 three
> edit 7d5187087c79 3 four
> EOF
merging file
Editing (7d5187087c79), commit as needed now to split the change
(to edit 7d5187087c79, `hg histedit --continue` after making changes)
[240]
$ hg abort
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
saved backup bundle to $TESTTMP/foo/.hg/strip-backup/1d8f701c7b35-cf7be322-backup.hg
saved backup bundle to $TESTTMP/foo/.hg/strip-backup/5c0056670bce-b54b65d0-backup.hg
Test when `backup-bundle` config option is not enabled
Enable config option:
$ cat >>$HGRCPATH <<EOF
> [rewrite]
> backup-bundle = False
> EOF
$ hg histedit -r '36b4bdd91f5b' --commands - << EOF
> pick 36b4bdd91f5b 0 one
> pick 6153eb23e623 1 two
> roll 80d23dfa866d 2 three
> edit 7d5187087c79 3 four
> EOF
merging file
Editing (7d5187087c79), commit as needed now to split the change
(to edit 7d5187087c79, `hg histedit --continue` after making changes)
[240]
$ hg abort
1 files updated, 0 files merged, 0 files removed, 0 files unresolved