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
This tests if hgweb and hgwebdir still work if the REQUEST_URI variable is
no longer passed with the request. Instead, SCRIPT_NAME and PATH_INFO
should be used from d74fc8dec2b4 onward to route the request.
$ hg init repo
$ cd repo
$ echo foo > bar
$ hg add bar
$ hg commit -m "test"
$ hg tip
changeset: 0:61c9426e69fe
tag: tip
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: test
$ cat > request.py <<EOF
> import os
> import sys
> from mercurial import (
> hgweb,
> util,
> )
> stringio = util.stringio
>
> errors = stringio()
> input = stringio()
>
> def startrsp(status, headers):
> print('---- STATUS')
> print(status)
> print('---- HEADERS')
> print([i for i in headers if i[0] != 'ETag'])
> print('---- DATA')
> sys.stdout.flush()
> return output.write
>
> env = {
> 'wsgi.version': (1, 0),
> 'wsgi.url_scheme': 'http',
> 'wsgi.errors': errors,
> 'wsgi.input': input,
> 'wsgi.multithread': False,
> 'wsgi.multiprocess': False,
> 'wsgi.run_once': False,
> 'REQUEST_METHOD': 'GET',
> 'PATH_INFO': '/',
> 'SCRIPT_NAME': '',
> 'SERVER_NAME': '$LOCALIP',
> 'SERVER_PORT': os.environ['HGPORT'],
> 'SERVER_PROTOCOL': 'HTTP/1.0'
> }
>
> def process(app):
> try:
> stdout = sys.stdout.buffer
> except AttributeError:
> stdout = sys.stdout
> content = app(env, startrsp)
> stdout.write(output.getvalue())
> stdout.write(b''.join(content))
> stdout.flush()
> getattr(content, 'close', lambda : None)()
> if errors.getvalue():
> print('---- ERRORS')
> print(errors.getvalue())
> sys.stdout.flush()
>
> output = stringio()
> env['QUERY_STRING'] = 'style=atom'
> process(hgweb.hgweb(b'.', name=b'repo'))
>
> output = stringio()
> env['QUERY_STRING'] = 'style=raw'
> process(hgweb.hgwebdir({b'repo': b'.'}))
> EOF
$ "$PYTHON" request.py
---- STATUS
200 Script output follows
---- HEADERS
[('Content-Type', 'application/atom+xml; charset=ascii')]
---- DATA
<?xml version="1.0" encoding="ascii"?>
<feed xmlns="http://www.w3.org/2005/Atom">
<!-- Changelog -->
<id>http://$LOCALIP:$HGPORT/</id> (glob)
<link rel="self" href="http://$LOCALIP:$HGPORT/atom-log"/> (glob)
<link rel="alternate" href="http://$LOCALIP:$HGPORT/"/> (glob)
<title>repo Changelog</title>
<updated>1970-01-01T00:00:00+00:00</updated>
<entry>
<title>[default] test</title>
<id>http://$LOCALIP:$HGPORT/#changeset-61c9426e69fef294feed5e2bbfc97d39944a5b1c</id> (glob)
<link href="http://$LOCALIP:$HGPORT/rev/61c9426e69fe"/> (glob)
<author>
<name>test</name>
<email>test</email>
</author>
<updated>1970-01-01T00:00:00+00:00</updated>
<published>1970-01-01T00:00:00+00:00</published>
<content type="xhtml">
<table xmlns="http://www.w3.org/1999/xhtml">
<tr>
<th style="text-align:left;">changeset</th>
<td>61c9426e69fe</td>
</tr>
<tr>
<th style="text-align:left;">branch</th>
<td>default</td>
</tr>
<tr>
<th style="text-align:left;">bookmark</th>
<td></td>
</tr>
<tr>
<th style="text-align:left;">tag</th>
<td>tip</td>
</tr>
<tr>
<th style="text-align:left;">user</th>
<td>test</td>
</tr>
<tr>
<th style="text-align:left;vertical-align:top;">description</th>
<td>test</td>
</tr>
<tr>
<th style="text-align:left;vertical-align:top;">files</th>
<td>bar<br /></td>
</tr>
</table>
</content>
</entry>
</feed>
---- STATUS
200 Script output follows
---- HEADERS
[('Content-Type', 'text/plain; charset=ascii')]
---- DATA
/repo/
$ cd ..