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
Tests of the file helper tool
$ f -h
?sage: f [options] [filenames] (glob)
?ptions: (glob)
-h, --help show this help message and exit
-t, --type show file type (file or directory)
-m, --mode show file mode
-l, --links show number of links
-s, --size show size of file
-n NEWER, --newer=NEWER
check if file is newer (or same)
-r, --recurse recurse into directories
-S, --sha1 show sha1 hash of the content
--sha256 show sha256 hash of the content
-M, --md5 show md5 hash of the content
-D, --dump dump file content
-H, --hexdump hexdump file content
-B BYTES, --bytes=BYTES
number of characters to dump
-L LINES, --lines=LINES
number of lines to dump
-q, --quiet no default output
$ mkdir dir
$ cd dir
$ f --size
size=0
$ echo hello | f --md5 --size
size=6, md5=b1946ac92492d2347c6235b4d2611184
$ f foo
foo: file not found
$ echo foo > foo
$ f foo
foo:
$ f --sha1 foo
foo: sha1=f1d2d2f924e986ac86fdf7b36c94bcdf32beec15
$ f --sha256 foo
foo: sha256=b5bb9d8014a0f9b1d61e21e796d78dccdf1352f23cd32812f4850b878ae4944c
#if symlink
$ f foo --mode
foo: mode=644
#endif
#if no-windows
$ "$PYTHON" $TESTDIR/seq.py 10 > bar
#else
Convert CRLF -> LF for consistency
$ "$PYTHON" $TESTDIR/seq.py 10 | sed "s/$//" > bar
#endif
#if unix-permissions symlink
$ chmod +x bar
$ f bar --newer foo --mode --type --size --dump --links --bytes 7
bar: file, size=21, mode=755, links=1, newer than foo
>>>
1
2
3
4
<<< no trailing newline
#endif
#if unix-permissions
$ ln bar baz
$ f bar -n baz -l --hexdump -t --sha1 --lines=9 -B 20
bar: file, links=2, newer than baz, sha1=612ca68d0305c821750a
0000: 31 0a 32 0a 33 0a 34 0a 35 0a 36 0a 37 0a 38 0a |1.2.3.4.5.6.7.8.|
0010: 39 0a |9.|
$ rm baz
#endif
#if unix-permissions symlink
$ ln -s yadda l
$ f . --recurse -MStmsB4
.: directory with 3 files, mode=755
./bar: file, size=21, mode=755, md5=3b03, sha1=612c
./foo: file, size=4, mode=644, md5=d3b0, sha1=f1d2
./l: link, size=5, md5=2faa, sha1=af93
#endif
$ f --quiet bar -DL 3
1
2
3
$ cd ..
Yadda is a symlink
$ f -qr dir -HB 17
dir: directory with 3 files (symlink !)
dir: directory with 2 files (no-symlink !)
dir/bar:
0000: 31 0a 32 0a 33 0a 34 0a 35 0a 36 0a 37 0a 38 0a |1.2.3.4.5.6.7.8.|
0010: 39 |9|
dir/foo:
0000: 66 6f 6f 0a |foo.|
dir/l: (symlink !)
0000: 79 61 64 64 61 |yadda| (symlink !)