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
$ cat >> $HGRCPATH<<EOF
> [extensions]
> drawdag=$TESTDIR/drawdag.py
> [experimental]
> evolution=true
> EOF
$ reinit () {
> rm -rf .hg && hg init
> }
$ hg init
Test what said in drawdag.py docstring
$ hg debugdrawdag <<'EOS'
> c d
> |/
> b
> |
> a
> EOS
$ hg log -G -T '{rev} {desc} ({tags})'
o 3 d (d tip)
|
| o 2 c (c)
|/
o 1 b (b)
|
o 0 a (a)
$ hg debugdrawdag <<'EOS'
> foo bar bar foo
> | / | |
> ancestor(c,d) a baz
> EOS
$ hg log -G -T '{desc}'
o foo
|\
+---o bar
| | |
| o | baz
| /
+---o d
| |
+---o c
| |
o | b
|/
o a
$ reinit
$ hg debugdrawdag <<'EOS'
> o foo
> |\
> +---o bar
> | | |
> | o | baz
> | /
> +---o d
> | |
> +---o c
> | |
> o | b
> |/
> o a
> EOS
$ hg log -G -T '{desc}'
o foo
|\
| | o d
| |/
| | o c
| |/
| | o bar
| |/|
| o | b
| |/
o / baz
/
o a
$ reinit
$ hg debugdrawdag <<'EOS'
> o foo
> |\
> | | o d
> | |/
> | | o c
> | |/
> | | o bar
> | |/|
> | o | b
> | |/
> o / baz
> /
> o a
> EOS
$ hg log -G -T '{desc}'
o foo
|\
| | o d
| |/
| | o c
| |/
| | o bar
| |/|
| o | b
| |/
o / baz
/
o a
$ hg manifest -r a
a
$ hg manifest -r b
a
b
$ hg manifest -r bar
a
b
$ hg manifest -r foo
a
b
baz
Edges existed in repo are no-ops
$ reinit
$ hg debugdrawdag <<'EOS'
> B C C
> | | |
> A A B
> EOS
$ hg log -G -T '{desc}'
o C
|\
| o B
|/
o A
$ hg debugdrawdag <<'EOS'
> C D C
> | | |
> B B A
> EOS
$ hg log -G -T '{desc}'
o D
|
| o C
|/|
o | B
|/
o A
Node with more than 2 parents are disallowed
$ hg debugdrawdag <<'EOS'
> A
> /|\
> D B C
> EOS
abort: A: too many parents: C D B
[255]
Cycles are disallowed
$ hg debugdrawdag <<'EOS'
> A
> |
> A
> EOS
abort: the graph has cycles
[255]
$ hg debugdrawdag <<'EOS'
> A
> |
> B
> |
> A
> EOS
abort: the graph has cycles
[255]
Create obsmarkers via comments
$ reinit
$ hg debugdrawdag <<'EOS'
> G
> |
> I D C F # split: B -> E, F, G
> \ \| | # replace: C -> D -> H
> H B E # prune: F, I
> \|/
> A
> EOS
1 new orphan changesets
$ hg log -r 'sort(all(), topo)' -G --hidden -T '{desc} {node}'
* G 711f53bbef0bebd12eb6f0511d5e2e998b984846
|
x F 64a8289d249234b9886244d379f15e6b650b28e3
|
o E 7fb047a69f220c21711122dfd94305a9efb60cba
|
| x D be0ef73c17ade3fc89dc41701eb9fc3a91b58282
| |
| | x C 26805aba1e600a82e93661149f2313866a221a7b
| |/
| x B 112478962961147124edd43549aedd1a335e44bf
|/
| x I 58e6b987bf7045fcd9c54f496396ca1d1fc81047
| |
| o H 575c4b5ec114d64b681d33f8792853568bfb2b2c
|/
o A 426bada5c67598ca65036d57d9e4b64b0c1ce7a0
$ hg debugobsolete
112478962961147124edd43549aedd1a335e44bf 7fb047a69f220c21711122dfd94305a9efb60cba 64a8289d249234b9886244d379f15e6b650b28e3 711f53bbef0bebd12eb6f0511d5e2e998b984846 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '0', 'operation': 'split', 'user': 'test'}
26805aba1e600a82e93661149f2313866a221a7b be0ef73c17ade3fc89dc41701eb9fc3a91b58282 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '9', 'operation': 'replace', 'user': 'test'}
be0ef73c17ade3fc89dc41701eb9fc3a91b58282 575c4b5ec114d64b681d33f8792853568bfb2b2c 0 (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '13', 'operation': 'replace', 'user': 'test'}
64a8289d249234b9886244d379f15e6b650b28e3 0 {7fb047a69f220c21711122dfd94305a9efb60cba} (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '0', 'operation': 'prune', 'user': 'test'}
58e6b987bf7045fcd9c54f496396ca1d1fc81047 0 {575c4b5ec114d64b681d33f8792853568bfb2b2c} (Thu Jan 01 00:00:00 1970 +0000) {'ef1': '0', 'operation': 'prune', 'user': 'test'}
Change file contents via comments
$ reinit
$ hg debugdrawdag <<'EOS'
> C # A/dir1/a = 1\n2
> |\ # B/dir2/b = 34
> A B # C/dir1/c = 5
> # C/dir2/c = 6
> # C/A = a
> # C/B = b
> EOS
$ hg log -G -T '{desc} {files}'
o C A B dir1/c dir2/c
|\
| o B B dir2/b
|
o A A dir1/a
$ for f in `hg files -r C`; do
> echo FILE "$f"
> hg cat -r C "$f"
> echo
> done
FILE A
a
FILE B
b
FILE dir1/a
1
2
FILE dir1/c
5
FILE dir2/b
34
FILE dir2/c
6