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.
$ cat >> $HGRCPATH <<EOF
> [extensions]
> rebase=
>
> [phases]
> publish=False
>
> [alias]
> tglog = log -G --template "{rev}:{phase} '{desc}' {branches}\n"
> EOF
$ hg init a
$ cd a
$ echo A > A
$ hg add A
$ hg ci -m A
$ echo 'B' > B
$ hg add B
$ hg ci -m B
$ echo C >> A
$ hg ci -m C
$ hg up -q -C 0
$ echo D >> A
$ hg ci -m D
created new head
$ echo E > E
$ hg add E
$ hg ci -m E
$ hg up -q -C 0
$ hg branch 'notdefault'
marked working directory as branch notdefault
(branches are permanent and global, did you want a bookmark?)
$ echo F >> A
$ hg ci -m F
$ cd ..
Rebasing B onto E - check keep: and phases
$ hg clone -q -u . a a1
$ cd a1
$ hg phase --force --secret 2
$ hg tglog
@ 5:draft 'F' notdefault
|
| o 4:draft 'E'
| |
| o 3:draft 'D'
|/
| o 2:secret 'C'
| |
| o 1:draft 'B'
|/
o 0:draft 'A'
$ hg rebase -s 1 -d 4 --keep
rebasing 1:27547f69f254 "B"
rebasing 2:965c486023db "C"
merging A
warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
unresolved conflicts (see hg resolve, then hg rebase --continue)
[1]
Solve the conflict and go on:
$ echo 'conflict solved' > A
$ rm A.orig
$ hg resolve -m A
(no more unresolved files)
continue: hg rebase --continue
$ hg rebase --continue
already rebased 1:27547f69f254 "B" as 45396c49d53b
rebasing 2:965c486023db "C"
$ hg tglog
o 7:secret 'C'
|
o 6:draft 'B'
|
| @ 5:draft 'F' notdefault
| |
o | 4:draft 'E'
| |
o | 3:draft 'D'
|/
| o 2:secret 'C'
| |
| o 1:draft 'B'
|/
o 0:draft 'A'
$ cd ..
Rebase F onto E - check keepbranches:
$ hg clone -q -u . a a2
$ cd a2
$ hg phase --force --secret 2
$ hg tglog
@ 5:draft 'F' notdefault
|
| o 4:draft 'E'
| |
| o 3:draft 'D'
|/
| o 2:secret 'C'
| |
| o 1:draft 'B'
|/
o 0:draft 'A'
$ hg rebase -s 5 -d 4 --keepbranches
rebasing 5:01e6ebbd8272 "F" (tip)
merging A
warning: conflicts while merging A! (edit, then use 'hg resolve --mark')
unresolved conflicts (see hg resolve, then hg rebase --continue)
[1]
Solve the conflict and go on:
$ echo 'conflict solved' > A
$ rm A.orig
$ hg resolve -m A
(no more unresolved files)
continue: hg rebase --continue
$ hg rebase --continue
rebasing 5:01e6ebbd8272 "F" (tip)
saved backup bundle to $TESTTMP/a2/.hg/strip-backup/01e6ebbd8272-6fd3a015-backup.hg (glob)
$ hg tglog
@ 5:draft 'F' notdefault
|
o 4:draft 'E'
|
o 3:draft 'D'
|
| o 2:secret 'C'
| |
| o 1:draft 'B'
|/
o 0:draft 'A'
$ cd ..