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
#require serve
$ cat <<EOF >> $HGRCPATH
> [extensions]
> schemes=
>
> [schemes]
> l = http://localhost:$HGPORT/
> parts = http://{1}:$HGPORT/
> z = file:\$PWD/
> EOF
$ hg init test
$ cd test
$ echo a > a
$ hg ci -Am initial
adding a
invalid scheme
$ hg log -R z:z
abort: no '://' in scheme url 'z:z'
[255]
http scheme
$ hg serve -n test -p $HGPORT -d --pid-file=hg.pid -A access.log -E errors.log
$ cat hg.pid >> $DAEMON_PIDS
$ hg incoming l://
comparing with l://
searching for changes
no changes found
[1]
check that {1} syntax works
$ hg incoming --debug parts://localhost
using http://localhost:$HGPORT/
sending capabilities command
comparing with parts://localhost/
query 1; heads
sending batch command
searching for changes
all remote heads known locally
no changes found
(sent 2 HTTP requests and * bytes; received * bytes in responses) (glob)
[1]
check that paths are expanded
$ PWD=`pwd` hg incoming z://
comparing with z://
searching for changes
no changes found
[1]
check that debugexpandscheme outputs the canonical form
$ hg debugexpandscheme bb://user/repo
https://bitbucket.org/user/repo
expanding an unknown scheme emits the input
$ hg debugexpandscheme foobar://this/that
foobar://this/that
expanding a canonical URL emits the input
$ hg debugexpandscheme https://bitbucket.org/user/repo
https://bitbucket.org/user/repo
errors
$ cat errors.log
$ cd ..