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 cvs no-root
This is https://bz.mercurial-scm.org/1148
and https://bz.mercurial-scm.org/1447
$ cvscall()
> {
> cvs -f "$@" > /dev/null
> }
$ cat <<EOF >> $HGRCPATH
> [extensions]
> convert =
> [convert]
> cvsps.cache = 0
> EOF
create cvs repository
$ mkdir cvsrepo
$ cd cvsrepo
$ CVSROOT=`pwd`
$ export CVSROOT
$ CVS_OPTIONS=-f
$ export CVS_OPTIONS
$ cd ..
$ rmdir cvsrepo
$ cvscall -q -d "$CVSROOT" init
Create a new project
$ mkdir src
$ cd src
$ echo "1" > a
$ echo "1" > b
$ cvscall import -m "init" src v0 r0 | sort
$ cd ..
$ cvscall co src
cvs checkout: Updating src
$ cd src
Branch the project
$ cvscall tag -b BRANCH
cvs tag: Tagging .
$ cvscall up -r BRANCH > /dev/null
cvs update: Updating .
Modify file a, then b, then a
$ sleep 1
$ echo "2" > a
$ cvscall ci -m "mod a"
cvs commit: Examining .
$ echo "2" > b
$ cvscall ci -m "mod b"
cvs commit: Examining .
$ sleep 1
$ echo "3" > a
$ cvscall ci -m "mod a again"
cvs commit: Examining .
Convert
$ cd ..
$ hg convert src
assuming destination src-hg
initializing destination src-hg repository
connecting to $TESTTMP/cvsrepo
scanning source...
collecting CVS rlog
7 log entries
creating changesets
5 changeset entries
sorting...
converting...
4 Initial revision
3 init
2 mod a
1 mod b
0 mod a again
updating tags
Check the result
$ hg -R src-hg log -G --template '{rev} ({branches}) {desc} files: {files}\n'
o 5 () update tags files: .hgtags
|
| o 4 (BRANCH) mod a again files: a
| |
| o 3 (BRANCH) mod b files: b
| |
| o 2 (BRANCH) mod a files: a
| |
| o 1 (v0) init files:
|/
o 0 () Initial revision files: a b
issue 1447
$ cvscall()
> {
> cvs -f "$@" > /dev/null
> sleep 1
> }
$ cvsci()
> {
> cvs -f ci "$@" >/dev/null
> sleep 1
> }
$ cvscall -Q -d `pwd`/cvsmaster2 init
$ cd cvsmaster2
$ CVSROOT=`pwd`
$ export CVSROOT
$ mkdir foo
$ cd ..
$ cvscall -Q co -d cvswork2 foo
$ cd cvswork2
$ echo foo > a.txt
$ echo bar > b.txt
$ cvscall -Q add a.txt b.txt
$ cvsci -m "Initial commit"
cvs commit: Examining .
$ echo foo > b.txt
$ cvsci -m "Fix b on HEAD"
cvs commit: Examining .
$ echo bar > a.txt
$ cvsci -m "Small fix in a on HEAD"
cvs commit: Examining .
$ cvscall -Q tag -b BRANCH
$ cvscall -Q up -P -rBRANCH
$ echo baz > b.txt
$ cvsci -m "Change on BRANCH in b"
cvs commit: Examining .
$ hg debugcvsps -x --parents foo
collecting CVS rlog
5 log entries
creating changesets
4 changeset entries
---------------------
PatchSet 1
Date: * (glob)
Author: * (glob)
Branch: HEAD
Tag: (none)
Log:
Initial commit
Members:
a.txt:INITIAL->1.1
b.txt:INITIAL->1.1
---------------------
PatchSet 2
Date: * (glob)
Author: * (glob)
Branch: HEAD
Tag: (none)
Branchpoints: BRANCH
Parent: 1
Log:
Fix b on HEAD
Members:
b.txt:1.1->1.2
---------------------
PatchSet 3
Date: * (glob)
Author: * (glob)
Branch: HEAD
Tag: (none)
Branchpoints: BRANCH
Parent: 2
Log:
Small fix in a on HEAD
Members:
a.txt:1.1->1.2
---------------------
PatchSet 4
Date: * (glob)
Author: * (glob)
Branch: BRANCH
Tag: (none)
Parent: 3
Log:
Change on BRANCH in b
Members:
b.txt:1.2->1.2.2.1
$ cd ..