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revlog: change generaldelta delta parent heuristic...
revlog: change generaldelta delta parent heuristic The old generaldelta heuristic was "if p1 (or p2) was closer than the last full text, use it, otherwise use prev". This was problematic when a repo contained multiple branches that were very different. If commits to branch A were pushed, and the last full text was branch B, it would generate a fulltext. Then if branch B was pushed, it would generate another fulltext. The problem is that the last fulltext (and delta'ing against `prev` in general) has no correlation with the contents of the incoming revision, and therefore will always have degenerate cases. According to the blame, that algorithm was chosen to minimize the chain length. Since there is already code that protects against that (the delta-vs-fulltext code), and since it has been improved since the original generaldelta algorithm went in (2011), I believe the chain length criteria will still be preserved. The new algorithm always diffs against p1 (or p2 if it's closer), unless the resulting delta will fail the delta-vs-fulltext check, in which case we delta against prev. Some before and after stats on manifest.d size. internal large repo old heuristic - 2.0 GB new heuristic - 1.2 GB mozilla-central old heuristic - 242 MB new heuristic - 261 MB The regression in mozilla central is due to the new heuristic choosing p2r as the delta when it's closer to the tip. Switching the algorithm to always prefer p1r brings the size back down (242 MB). This is result of the way in which mozilla does merges and pushes, and the result could easily swing the other direction in other repos (depending on if they merge X into Y or Y into X), but will never be as degenerate as before. I future patch will address the regression by introducing an optional, even more aggressive delta heuristic which will knock the mozilla manifest size down dramatically.

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ReadMe.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>Mercurial for Windows</title>
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<h1>Mercurial for Windows</h1>
<p>Welcome to Mercurial for Windows!</p>
<p>
Mercurial is a command-line application. You must run it from
the Windows command prompt (or if you're hard core, a <a
href="http://www.mingw.org/">MinGW</a> shell).
</p>
<p class="indented">
<i>Note: the standard <a href="http://www.mingw.org/">MinGW</a>
msys startup script uses rxvt which has problems setting up
standard input and output. Running bash directly works
correctly.</i>
</p>
<p>
For documentation, please visit the <a
href="http://mercurial.selenic.com/">Mercurial web site</a>.
You can also download a free book, <a
href="http://hgbook.red-bean.com/">Mercurial: The Definitive
Guide</a>.
</p>
<p>
By default, Mercurial installs to <tt>C:\Program
Files\Mercurial</tt>. The Mercurial command is called
<tt>hg.exe</tt>.
</p>
<h1>Testing Mercurial after you've installed it</h1>
<p>
The easiest way to check that Mercurial is installed properly is
to just type the following at the command prompt:
</p>
<pre>
hg
</pre>
<p>
This command should print a useful help message. If it does,
other Mercurial commands should work fine for you.
</p>
<h1>Configuration notes</h1>
<h4>Default editor</h4>
<p>
The default editor for commit messages is 'notepad'. You can set
the <tt>EDITOR</tt> (or <tt>HGEDITOR</tt>) environment variable
to specify your preference or set it in <tt>mercurial.ini</tt>:
</p>
<pre>
[ui]
editor = whatever
</pre>
<h4>Configuring a Merge program</h4>
<p>
It should be emphasized that Mercurial by itself doesn't attempt
to do a Merge at the file level, neither does it make any
attempt to Resolve the conflicts.
</p>
<p>
By default, Mercurial will use the merge program defined by the
<tt>HGMERGE</tt> environment variable, or uses the one defined
in the <tt>mercurial.ini</tt> file. (see <a
href="http://mercurial.selenic.com/wiki/MergeProgram">MergeProgram</a>
on the Mercurial Wiki for more information)
</p>
<h1>Reporting problems</h1>
<p>
Before you report any problems, please consult the <a
href="http://mercurial.selenic.com/">Mercurial web site</a>
and see if your question is already in our list of <a
href="http://mercurial.selenic.com/wiki/FAQ">Frequently
Answered Questions</a> (the "FAQ").
</p>
<p>
If you cannot find an answer to your question, please feel free
to send mail to the Mercurial mailing list, at <a
href="mailto:mercurial@selenic.com">mercurial@selenic.com</a>.
<b>Remember</b>, the more useful information you include in your
report, the easier it will be for us to help you!
</p>
<p>
If you are IRC-savvy, that's usually the fastest way to get
help. Go to <tt>#mercurial</tt> on <tt>irc.freenode.net</tt>.
</p>
<h1>Author and copyright information</h1>
<p>
Mercurial was written by <a href="http://www.selenic.com">Matt
Mackall</a>, and is maintained by Matt and a team of volunteers.
</p>
<p>
The Windows installer was written by <a
href="http://www.serpentine.com/blog">Bryan O'Sullivan</a>.
</p>
<p>
Mercurial is Copyright 2005-2015 Matt Mackall and others. See
the <tt>Contributors.txt</tt> file for a list of contributors.
</p>
<p>
Mercurial is free software; you can redistribute it and/or
modify it under the terms of the <a
href="http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt">GNU
General Public License version 2</a> or any later version.
</p>
<p>
Mercurial is distributed in the hope that it will be useful, but
<b>without any warranty</b>; without even the implied warranty
of <b>merchantability</b> or <b>fitness for a particular
purpose</b>. See the GNU General Public License for more
details.
</p>
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