bdiff: balance recursion to avoid quadratic behavior (issue4704)
For highly structured files like JSON or XML dumps with large numbers
of duplicate lines (eg braces) and isolated matching lines, bdiff
could find large numbers of equally good spans. Because it prefers
earlier matches, this would result in pathologically unbalance
recursion that resulted in quadratic performance.
This patch makes it prefer matches closer to the middle that tend to
balance recursion. This change improves the speed of a pathological
test case from 1100s to 9s.
Included is a smaller test that has a roughly 50x safety margin on the
performance it accepts. It's likely to fail on pure builds because
difflib also has a recursion-balancing problem.
test stripping of filelogs where the linkrev doesn't always increase
$ echo '[extensions]' >> $HGRCPATH
$ echo 'strip =' >> $HGRCPATH
$ hg init orig
$ cd orig
$ commit()
> {
> hg up -qC null
> count=1
> for i in "$@"; do
> for f in $i; do
> echo $count > $f
> done
> count=`expr $count + 1`
> done
> hg commit -qAm "$*"
> }
2 1 0 2 0 1 2
$ commit '201 210'
$ commit '102 120' '210'
$ commit '021'
$ commit '201' '021 120'
$ commit '012 021' '102 201' '120 210'
$ commit 'manifest-file'
$ commit '102 120' '012 210' '021 201'
$ commit '201 210' '021 120' '012 102'
$ HGUSER=another-user; export HGUSER
$ commit 'manifest-file'
$ commit '012' 'manifest-file'
$ cd ..
$ hg clone -q -U -r -1 -r -2 -r -3 -r -4 -r -6 orig crossed
$ cd crossed
$ hg debugindex --manifest
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 112 ..... 0 6f105cbb914d 000000000000 000000000000 (re)
1 112 56 ..... 3 1b55917b3699 000000000000 000000000000 (re)
2 168 123 ..... 1 8f3d04e263e5 000000000000 000000000000 (re)
3 291 122 ..... 2 f0ef8726ac4f 000000000000 000000000000 (re)
4 413 87 ..... 4 0b76e38b4070 000000000000 000000000000 (re)
$ for i in 012 021 102 120 201 210 manifest-file; do
> echo $i
> hg debugindex $i
> echo
> done
012
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 3 ..... 0 b8e02f643373 000000000000 000000000000 (re)
1 3 3 ..... 1 5d9299349fc0 000000000000 000000000000 (re)
2 6 3 ..... 2 2661d26c6496 000000000000 000000000000 (re)
021
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 3 ..... 0 b8e02f643373 000000000000 000000000000 (re)
1 3 3 ..... 2 5d9299349fc0 000000000000 000000000000 (re)
2 6 3 ..... 1 2661d26c6496 000000000000 000000000000 (re)
102
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 3 ..... 1 b8e02f643373 000000000000 000000000000 (re)
1 3 3 ..... 0 5d9299349fc0 000000000000 000000000000 (re)
2 6 3 ..... 2 2661d26c6496 000000000000 000000000000 (re)
120
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 3 ..... 1 b8e02f643373 000000000000 000000000000 (re)
1 3 3 ..... 2 5d9299349fc0 000000000000 000000000000 (re)
2 6 3 ..... 0 2661d26c6496 000000000000 000000000000 (re)
201
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 3 ..... 2 b8e02f643373 000000000000 000000000000 (re)
1 3 3 ..... 0 5d9299349fc0 000000000000 000000000000 (re)
2 6 3 ..... 1 2661d26c6496 000000000000 000000000000 (re)
210
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 3 ..... 2 b8e02f643373 000000000000 000000000000 (re)
1 3 3 ..... 1 5d9299349fc0 000000000000 000000000000 (re)
2 6 3 ..... 0 2661d26c6496 000000000000 000000000000 (re)
manifest-file
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 3 ..... 3 b8e02f643373 000000000000 000000000000 (re)
1 3 3 ..... 4 5d9299349fc0 000000000000 000000000000 (re)
$ cd ..
$ for i in 0 1 2 3 4; do
> hg clone -q -U --pull crossed $i
> echo "% Trying to strip revision $i"
> hg --cwd $i strip $i
> echo "% Verifying"
> hg --cwd $i verify
> echo
> done
% Trying to strip revision 0
saved backup bundle to $TESTTMP/0/.hg/strip-backup/*-backup.hg (glob)
% Verifying
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
7 files, 4 changesets, 15 total revisions
% Trying to strip revision 1
saved backup bundle to $TESTTMP/1/.hg/strip-backup/*-backup.hg (glob)
% Verifying
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
7 files, 4 changesets, 14 total revisions
% Trying to strip revision 2
saved backup bundle to $TESTTMP/2/.hg/strip-backup/*-backup.hg (glob)
% Verifying
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
7 files, 4 changesets, 14 total revisions
% Trying to strip revision 3
saved backup bundle to $TESTTMP/3/.hg/strip-backup/*-backup.hg (glob)
% Verifying
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
7 files, 4 changesets, 19 total revisions
% Trying to strip revision 4
saved backup bundle to $TESTTMP/4/.hg/strip-backup/*-backup.hg (glob)
% Verifying
checking changesets
checking manifests
crosschecking files in changesets and manifests
checking files
7 files, 4 changesets, 19 total revisions