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<!DOCTYPE html>
<html>
<head>
<title>Presentation</title>
<meta charset='utf-8'>
<script
src='js/slides.js'></script>
<style>
section {
counter-reset: section;
}
article {
counter-increment:section;
}
article:not(.nocounter):after {
content: counter(section);
bottom: 1em;
position: absolute;
display: block;
}
</style>
</head>
<body style='display: none'>
<section class='slides layout-regular template-default'>
<article class="nocounter">
<h1>
VCS Interoperability
</h1>
<p>
David Barr
<br>
Jan 20, 2012
</p>
<p>
<img src="img/git_logo_192x106.jpg" style="vertical-align:middle;" alt="git">
&
<img src="img/subversion_logo1.png" style="vertical-align:middle;height:162px;width:143px" alt="Subversion">
</p>
</article>
<article>
<h3>
Scratching one's itch
</h3>
<p>Project at $JOB, March 2010 — 5 years, 22000 commits, 2.8GB
<ul>
<li><em>git-svn</em> — 4 days, NN GB RAM, failed at 90%
<li><em>svn-all-fast-export</em> — skip 3 commits or spew indefinitely
<li><em>svn2git.py</em> — quick for 50% then slowed to glacial pace
</ul>
</p>
<p><strong>Complete and timely conversion impossible!</strong></p>
</article>
<article>
<h3>
Sufficiently numerous anecdotes are data
</h3>
<p>Maybe it's not just my repository?</p>
<p>Reached out to the git community for anecdotes</p>
<p>Came with a proposal in hand</p>
</article>
<article>
<h3>
Saved the world in less than 30 days
</h3>
<p>Jokes, lol</p>
</article>
<article>
<h3>
OK, so it was hard. Why?
</h3>
<p>Mapping Subversion history to git DAG non-trivial
<ul>
<li>Empty directories
<li>File permissions
<li>Symlink representation
<li>Commit and file metadata
</ul>
</p>
</article>
<article>
<h3>
So what was the proposal?
</h3>
<p>Translator — Subversion dump to git fast-import</p>
<p>Data structure that maps between them and scales linearly<p>
<p>Independent of both projects</p>
<p>Merged <em>svn-dump-fast-export</em> into git-contrib as <em>svn-fe</em>
</article>
<article>
<h3>
Sounds easy, why more than 30 days?
</h3>
<p>Although it 'uses only timeless fs concepts', verbs in Subversion dump format not clearly defined.
<ul>
<li>change
<li>add
<li>delete
<li>replace
</ul>
</p>
<p>The obvious one was delete, the rest full of surprises.</p>
<p>Thus began a 3 month protocol reverse-engineering effort.</p>
</article>
<article>
<h3>
So we have a translator, how is it fed?
</h3>
<p>Extracting complete history from Subversion server is hard.
<ul>
<li><em>svnsync</em> + <em>svnadmin dump</em>
<li><em>svk sync</em> + <em>svk admin dump</em>
</ul>
</p>
<p>For large repositories, ask for a compressed dump.</p>
<p>Enter <em>svnrdump</em>, the product of Ram's GSoC 2010 project.</p>
</article>
<article>
<h3>
<em>svnrdump</em> — Google Summer of Code 2010
</h3>
<h4>Ramkumar Ramachandra</h4>
<p>
<ul>
<li>First-class Subversion tool
<li><em>svnrdump dump</em>
<li><em>svnrdump load</em>
<li>General purpose tool suitable for *Nix style interaction
</ul>
</p>
</article>
<article>
<h3>
Any issues with <em>git fast-import</em>?
</h3>
<p>Protocol extensions for bi-directional communication
<ul>
<li><em>cat-blob</em> — read existing or imported blob data
<li><em>ls</em> — inspect active commit or named trees
</ul>
</p>
<p>Complexity can be removed from the translator.</p>
<p>Applying Subversion binary deltas becomes straightforward.</p>
</article>
<article>
<h3>
<em>git-remote-svn</em> — Google Summer of Code 2011
</h3>
<h4>Dmitry Ivankov</h4>
<p>
<ul>
<li><em>svn-fe</em> additional command-line flags
<li><em>git-remote-svn</em> wrapper in Python
<li>Numerous bug fixes for <em>git fast-import</em>
<li>Documentation fixes for <em>git fast-import</em>
<li>Use <em>cat-blob</em> as a hint for delta computation
</ul>
</p>
</article>
<article>
<h3>
<em>remote-helper</em> improvements
</h3>
<h4>
Sverre Rabbelier, Jeff King, et al.
</h4>
<p>In parallel to all this work, there were many improvements to the remote helper infrastructure which would ultimately be used to integrate the translator into the natural git flow.</p>
<p>Jérémie Nikaes' <em>git-remote-mediawiki</em> helped spur things along.</p>
</article>
<article>
<h3>
Future work
</h3>
<p>
<ul>
<li>Merge outstanding GSoC patches into git-core
<li>Upstream <em>vcs-svn</em> from git-core to <em>svn-dump-fast-export</em>
<li>Implement <em>fast-import</em> protocol extensions for <em>hg</em> or <em>bzr</em>
<li>Reverse translator to enable writing to Subversion
<li>Integrate svn-dump-fast-export with <em>hg</em> or <em>bzr</em>
</p>
</article>
<article>
<h3>
Merge outstanding GSoC patches into git-core
</h3>
<p>
<ul>
<li>90+ patches not yet merged into jch/master
<li>prioritise topics and reorder for submission
<li>garner support for inclusion
</ul>
</p>
</article>
<article>
<h3>
Upstream <em>vcs-svn</em> from git-core to <em>svn-dump-fast-export</em>
</h3>
</article>
<article>
<h3>
Implement <em>fast-import</em> protocol extensions for <em>hg</em> or <em>bzr</em>
</h3>
</article>
<article>
<h3>
Reverse translator to enable writing to Subversion
</h3>
</article>
<article>
<h3>
Integrate svn-dump-fast-export with <em>hg</em> or <em>bzr</em>
</h3>
</article>
<article class="nocounter">
<h3>
Questions & Answers
</h3>
</article>
<article class="nocounter">
<h3>
Thank you
</h3>
<p>For more information or to get involved email <em>b@rr-dav.id.au</em> and consider cc'ing <em>git@vger.kernel.org</em></p>
<p>Git Logo and Icon by Dylan Beattie distributed under <a href="http://creativecommons.org/licenses/by-sa/3.0/" target="_blank">Creative Commons Attribution-ShareAlike 3.0 Unported License</a>.</p>
</article>
</section>
</body>
</html>