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
====================================
Testing head checking code: Case D-6
====================================
Mercurial checks for the introduction of new heads on push. Evolution comes
into play to detect if existing branches on the server are being replaced by
some of the new one we push.
This case is part of a series of tests checking this behavior.
Category D: remote head is "obs-affected" locally, but result is not part of the push
TestCase 6: single changeset, superseeded then pruned (on a new changeset unpushed) changeset
This is a partial push variation of case B-6
.. old-state:
..
.. * 1 changeset branch
..
.. new-state:
..
.. * old branch is rewritten onto another one,
.. * the new version is then pruned.
..
.. expected-result:
..
.. * push denied
..
.. graph-summary:
..
.. A ø⇠⊗ A'
.. | |
.. C ◔ | ○ B
.. \|/
.. ●
$ . $TESTDIR/testlib/push-checkheads-util.sh
Test setup
----------
$ mkdir D6
$ cd D6
$ setuprepos
creating basic server and client repo
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd client
$ hg up 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ mkcommit B0
created new head
$ mkcommit A1
$ hg up '0'
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
$ mkcommit C0
created new head
$ hg debugobsolete `getid "desc(A0)"` `getid "desc(A1)"`
1 new obsolescence markers
obsoleted 1 changesets
$ hg debugobsolete --record-parents `getid "desc(A1)"`
1 new obsolescence markers
obsoleted 1 changesets
$ hg log -G --hidden
@ 0f88766e02d6 (draft): C0
|
| x ba93660aff8d (draft): A1
| |
| o 74ff5441d343 (draft): B0
|/
| x 8aaa48160adc (draft): A0
|/
o 1e4be0697311 (public): root
Actual testing
--------------
$ hg push --rev 'desc(C0)'
pushing to $TESTTMP/D6/server
searching for changes
abort: push creates new remote head 0f88766e02d6
(merge or see 'hg help push' for details about pushing new heads)
[20]
$ cd ../..