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    <title>Introduction to Distributed Version Control with Mercurial</title>
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            <header><h1>Introduction to Distributed Version Control with Mercurial</h1></header>


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            <header><h1>Agenda</h1></header>


            <section><ul class="simple">
<li>Brief history of version control tools</li>
<li>Features of distributed version control</li>
<li>Brief introduction to Mercurial</li>
</ul></section>

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            <header><h1># whoami</h1></header>


            <section><p>Brian Neal &lt;<a class="reference external" href="mailto:bgneal1&#64;rockwellcollins.com">bgneal1&#64;rockwellcollins.com</a>&gt;</p>
<p>Started at Rockwell Collins in July 1999</p>
<p>You might remember me from the following programs:</p>
<ul class="simple">
<li>UMS (July 1999 - Spring 2000)</li>
<li>Surgical Strike - (Spring - Fall 2000)</li>
<li>JTRS 2B - (Fall 2000 - Summer 2001)</li>
<li>SCAMP SEP - (Summer 2001 - October 2004)</li>
<li>TTNT (January 2005 - Present)</li>
</ul></section>

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            <header><h1>Disclaimers</h1></header>


            <section><ul class="simple">
<li>This is not a sales pitch</li>
<li>I actually <span class="strike">like</span> respect Subversion<ul>
<li>I'm the &quot;Subversion guy&quot; on my team</li>
<li>I developed SVN training and have given it ~9-10 times</li>
<li><a class="reference external" href="http://subversion.tigris.org/issues/show_bug.cgi?id=3919">http://subversion.tigris.org/issues/show_bug.cgi?id=3919</a></li>
</ul>
</li>
<li>I am not an expert<ul>
<li>I'm probably making this look too easy</li>
</ul>
</li>
</ul></section>

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            <header><h1>Why learn about DVCS?</h1></header>


            <section><ul class="simple">
<li>DVCS have exploded in the open source world<ul>
<li>Interestingly, Subversion is growing in corporate environments</li>
</ul>
</li>
<li>Frustration with current tools</li>
<li>Interesting to see how the tools have evolved<ul>
<li>As a software practitioner, you should know what your options are</li>
</ul>
</li>
</ul></section>

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            <header><h1>Brief History of Version Control Tools</h1></header>


            <section><h2>First Generation</h2>
<ul class="simple">
<li>No networking!</li>
<li>Concurrency method: locks</li>
<li>Examples:<ul>
<li>SCCS - 1972</li>
<li>RCS - 1982</li>
</ul>
</li>
</ul></section>

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            <header><h1>Brief History of Version Control Tools</h1></header>


            <section><h2>Second Generation</h2>
<ul class="simple">
<li>Client/Server networking; CVCS (Centralized Version Control)</li>
<li>Concurrency method: merge before commit</li>
<li>Examples:<ul>
<li>CVS - 1990</li>
<li>IBM Rational ClearCase - 1992</li>
<li>Visual SourceSafe - 1994</li>
<li>Perforce - 1995</li>
<li>SVN - 2000</li>
</ul>
</li>
</ul></section>

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            <header><h1>Brief History of Version Control Tools</h1></header>


            <section><h2>Third Generation</h2>
<ul class="simple">
<li>Distributed networking; DVCS (Distributed Version Control)</li>
<li>Concurrency method: commit then merge</li>
<li>Examples:<ul>
<li>Bitkeeper - 2000</li>
<li>Darcs - 2003</li>
<li>Monotone - 2003</li>
<li>Git - 2005</li>
<li><strong>Mercurial</strong> - 2005</li>
<li>Fossil - 2006</li>
<li>Bazaar - 2007</li>
<li>Veracity - 2011</li>
</ul>
</li>
</ul></section>

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            <header><h1>What is a CVCS Again?</h1></header>


            <section><img alt="images/cvcs.png" src="images/cvcs.png" /></section>

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            <header><h1>So what's a DVCS look like?</h1></header>


            <section><img alt="images/dvcs.png" src="images/dvcs.png" />
<p>All repositories are peers. By convention only, one repository is designated the master.
It is possible for all peers to exchange changes (via <em>push</em> and <em>pull</em> operations).</p></section>

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            <header><h1>What does a DVCS buy you?</h1></header>


            <section><ul class="simple">
<li>Private workspaces</li>
<li>Offline mode</li>
<li>Speed</li>
<li>Scalability</li>
<li>Split Geography</li>
<li>Flexible workflows</li>
<li>Distributed backups</li>
<li><strong>Easier merging</strong></li>
<li><strong>Commit before merge</strong></li>
</ul></section>

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            <header><h1>Private Workspaces</h1></header>


            <section><ul class="simple">
<li>You can safely experiment in your local repository</li>
<li>Commit as often as you like without affecting the team<ul>
<li>Encourages &quot;micro-commits&quot;</li>
<li>With SVN, people often hold back until an entire feature is complete</li>
</ul>
</li>
<li>Encourages experimentation<ul>
<li>Make cheap repository clones to try things out</li>
<li>Not visible to coworkers</li>
</ul>
</li>
</ul></section>

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            <header><h1>Offline Mode</h1></header>


            <section><ul class="simple">
<li>Work when you have spotty or no network access</li>
<li>Full access to the repo when offline</li>
<li>Can work on multiple tasks offline</li>
</ul>
<blockquote>
<ul class="simple">
<li>Work on bug report #1</li>
<li>Commit</li>
<li>Work on bug report #2</li>
<li>With a CVCS, you'd have both fixes in the same pending commit</li>
</ul>
</blockquote></section>

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            <header><h1>Speed</h1></header>


            <section><ul class="simple">
<li>Local operations are <strong>fast</strong><ul>
<li>No, really, <strong>you will</strong> notice a big difference</li>
<li>Switching between branches will blow your mind</li>
</ul>
</li>
<li>Initial pull down of an entire repository <em>might</em> be slower than a CVCS<ul>
<li>Then again, you might be surprised</li>
<li>Mercurial, for example, stores an <em>entire</em> repository in less space than
a SVN working copy in many cases</li>
</ul>
</li>
</ul></section>

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            <header><h1>Scalability</h1></header>


            <section><ul class="simple">
<li>Some CVCS systems require heavy weight hardware to support the server<ul>
<li>E.g. ClearCase with a thousand users</li>
<li>With a DVCS, only pushes &amp; pulls contact a central server</li>
<li>Most of the work is done locally</li>
</ul>
</li>
</ul></section>

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            <header><h1>Split Geography</h1></header>


            <section><ul class="simple">
<li>Imagine a team split between Cedar Rapids &amp; Richardson...</li>
<li>With a CVCS, you have to pick where to put the server</li>
<li>The remote location is stuck with network latency &amp; associated problems</li>
<li>With a DVCS, each site can have a central repository<ul>
<li>The two central repos can be synch'ed when convenient or even scripted</li>
</ul>
</li>
</ul>
<img alt="images/split_geography.png" src="images/split_geography.png" /></section>

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            <header><h1>Flexible Workflows</h1></header>


            <section><ul class="simple">
<li>There is no internal concept of a central repository</li>
<li>A central repository exits only by convention</li>
<li>More elaborate topologies and workflows can be created:<ul>
<li>A SW team may push to a central SW repo</li>
<li>Periodically changes from the SW repo are pushed to a QA repo</li>
<li>Changes from the QA repo can be pushed into a release repo</li>
</ul>
</li>
</ul>
<img alt="images/flexible_workflows.png" src="images/flexible_workflows.png" /></section>

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            <header><h1>Distributed Backups</h1></header>


            <section><ul class="simple">
<li>With a DVCS, multiple copies of the repository exist on multiple machines</li>
<li><strong>Of course, this is no substitute for a real backup strategy!</strong></li>
<li>But usually, and with short notice, you can easily designate a repository as
the central repository in an emergency</li>
</ul></section>

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            <header><h1>Easier Merging</h1></header>


            <section><ul class="simple">
<li>Subversion has a bad reputation for merging<ul>
<li>Some of this is not warranted...<ul>
<li>Merge tracking was added in SVN v1.5</li>
<li>Steadily improved in v1.6 - v1.7</li>
</ul>
</li>
<li>SVN does not handle file renames and tree conflicts very well</li>
<li>A lot of teams simply avoid merging out of fear or superstition</li>
</ul>
</li>
</ul></section>

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            <header><h1>Easier Merging (cont.)</h1></header>


            <section><ul class="simple">
<li>Why is merging better in a DVCS?<ul>
<li>Merging simply has to work correctly and be easy in a DVCS<ul>
<li>More attention was paid to this aspect by DVCS's</li>
</ul>
</li>
<li>DVCS's use <strong>directed acyclic graphs</strong> internally to represent change sets<ul>
<li>More information is available to make merge decisions</li>
<li>Easier to find common ancestors of code</li>
</ul>
</li>
<li>Developer changes and merge changes are separate<ul>
<li>&quot;Commit before merge&quot;</li>
</ul>
</li>
</ul>
</li>
</ul></section>

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            <header><h1>Commit Before Merge</h1></header>


            <section><ul class="simple">
<li>With a CVCS:<ul>
<li>You make changes in your working copy</li>
<li>Before you can commit, you often must perform an update<ul>
<li>This may trigger a merge</li>
<li>Your changes are now mixed up with your friendly coworkers' changes</li>
<li>Sometimes this can be a problem...</li>
</ul>
</li>
</ul>
</li>
<li>With a DVCS:<ul>
<li>You make changes in your working copy</li>
<li>You commit locally!</li>
<li>You can then choose to pull changes from others and merge<ul>
<li><strong>Your changes are already safely tucked away and can be retrieved later if things go wrong</strong></li>
</ul>
</li>
</ul>
</li>
</ul></section>

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            <header><h1>Okay, what's the catch?</h1></header>


            <section><h2>Potential drawbacks to a DVCS</h2>
<ul class="simple">
<li>Practically no support for locks<ul>
<li>This makes working with binary files difficult in a team environment</li>
</ul>
</li>
<li>Huge repositories are not practical</li>
<li>Heterogeneous repositories are not practical<ul>
<li>Not a good idea to mix, say, software, systems, and firmware in the same repo</li>
<li>Not a good idea to mix multiple products in the same repo</li>
<li><em>Arguably, this applies to a CVCS as well</em></li>
</ul>
</li>
<li>No support for path-based access control<ul>
<li>With current tools, you either can access the full repo, or nothing</li>
</ul>
</li>
</ul></section>

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            <header><h1>Introduction to Mercurial</h1></header>


            <section><ul class="simple">
<li>Overview</li>
<li>Repositories &amp; working directories</li>
<li>Changesets</li>
<li>Branches &amp; Tags</li>
<li>Example workflow</li>
<li>Command overview</li>
</ul></section>

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            <header><h1>Mercurial Overview</h1></header>


            <section><ul class="simple">
<li>Distributed Version Control System</li>
<li>Free, open source software licensed under GPL Version 2</li>
<li>Available for Microsoft Windows, GNU/Linux, Mac OS X, Solaris 11 Express</li>
<li>Written in Python with a small amount of C</li>
<li>Extensible with official and 3rd party extensions</li>
<li>TortoiseHg is a popular GUI for Windows</li>
<li>Reputation for being fast &amp; easy to get started with</li>
<li>Can be served via Apache Web server</li>
<li>Repository hooks</li>
<li>Integrates with the Trac issue tracker</li>
<li>Can import history from other tools, including Subversion</li>
</ul></section>

          </div>
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            <header><h1>Presenter Notes</h1></header>
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            <header><h1>Repositories &amp; Working Directories</h1></header>


            <section><p>A repository consists of two things:</p>
<ul class="simple">
<li>Your working directory (similar to a working copy in SVN)</li>
<li>The repository itself (also known as &quot;the store&quot;)<ul>
<li>A .hg directory at the top of your working copy</li>
</ul>
</li>
</ul>
<p>Example:</p>
<pre class="literal-block">
$ ls -A
.hg  .hgignore  images/  slides.cfg  slides.css  slides.html  slides.rst
</pre>
<ul class="simple">
<li>Repositories communicate via the <em>push</em> and <em>pull</em> commands<ul>
<li>Push &amp; Pull do not affect your working directory<ul>
<li>An <em>update</em> or <em>merge</em> must be performed to receive remote changes into your working directory</li>
</ul>
</li>
</ul>
</li>
</ul></section>

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            <header><h1>Presenter Notes</h1></header>
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            <header><h1>What's in a Repository?</h1></header>


            <section><p>A repository consists of a directed, acyclic graph of <em>changesets</em></p>
<img alt="images/repos.png" src="images/repos.png" />
<ul class="simple">
<li>Each changeset can have 0, 1, or 2 parents (and infinite children)</li>
<li>A changeset with 0 parents is the root</li>
<li>A changeset with 2 parents is the result of a merge</li>
<li>The newest changeset is called the <em>tip</em>, a special tag name</li>
</ul></section>

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            <header><h1>What's a Changeset?</h1></header>


            <section><p>A changeset is an atomic collection of changes and some meta information.
The meta information includes:</p>
<ul class="simple">
<li>Who made the changes</li>
<li>When the changes were made</li>
<li>Why - the commit message</li>
<li>The name of the branch the changes were made on (&quot;default&quot; is the default)</li>
<li>A local revision number</li>
<li>A changeset ID; a 40 digit hex number (SHA-1 hash of the changeset &amp; parents)</li>
</ul>
<p>A changeset can be named by:</p>
<ul class="simple">
<li>Revision number (within a repository)</li>
<li>Changeset ID (globally)</li>
<li>Tag name</li>
</ul></section>

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            <header><h1>Presenter Notes</h1></header>
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            <header><h1>Branches &amp; Tags</h1></header>


            <section><ul class="simple">
<li>In the simple case, each changeset appear in a line</li>
<li>When a changeset develops 2 or more children, a branch occurs<ul>
<li>The latest revision of a branch is called a <em>head</em></li>
<li>A <em>merge</em> is when two branches join back together</li>
<li>Branches can be given names; the default branch name is <em>&quot;default&quot;</em></li>
</ul>
</li>
<li>Changesets can be given human readable names, or <em>tags</em><ul>
<li><em>Local tags</em> are only visible within a repository</li>
<li><em>Regular tags</em> are revision controlled and propagate to other repos</li>
<li>The newest head in a repository is a tag called <em>tip</em></li>
</ul>
</li>
</ul></section>

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            <header><h1>A note on branching...</h1></header>


            <section><ul class="simple">
<li>Branching happens <em>all the time</em> when multiple developers are involved</li>
<li>It is so natural you may not notice it at first</li>
<li>Branching often has two meanings:<ul>
<li>The &quot;normal&quot; day-to-day branching when developers combine changes</li>
<li>The conceptual branching that occurs when:<ul>
<li>You need a feature branch</li>
<li>You need a release branch</li>
<li>You need an experimental branch</li>
<li>etc.</li>
</ul>
</li>
</ul>
</li>
</ul></section>

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            <header><h1>Presenter Notes</h1></header>
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            <header><h1>Ways to Branch in Hg</h1></header>


            <section><ul class="simple">
<li>Just make another clone of the repository!<ul>
<li>Slowest, safest, easiest to understand</li>
<li>Hard links are used (where available) to minimize disk space</li>
</ul>
</li>
<li>Bookmarks<ul>
<li>Lightweight tags can be applied to changesets</li>
<li>Similar to how Git does branches</li>
<li>Bookmarks can be deleted; they are not permanent</li>
</ul>
</li>
<li>Named branches<ul>
<li>Actually recording the branch name in the changeset</li>
</ul>
</li>
<li>Anonymous branches<ul>
<li>Update to any old changeset, make changes, commit</li>
<li>&quot;Good&quot; for emergency fixes, bad for remembering what you did</li>
</ul>
</li>
</ul></section>

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            <header><h1>Presenter Notes</h1></header>
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            <header><h1>Example Workflow</h1></header>


            <section><img alt="images/workflow1.png" src="images/workflow1.png" /></section>

          </div>
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            <header><h1>Presenter Notes</h1></header>
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            <header><h1>Example Workflow (cont.)</h1></header>


            <section><img alt="images/workflow2.png" src="images/workflow2.png" /></section>

          </div>
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            <header><h1>Presenter Notes</h1></header>
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            <header><h1>Example Workflow (cont.)</h1></header>


            <section><img alt="images/workflow3.png" src="images/workflow3.png" />
<ul class="simple">
<li>Notice that after Alice's pull:<ul>
<li>Her working directory is unaffected</li>
<li>Her repository only has one head =&gt; no merging required</li>
</ul>
</li>
</ul></section>

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            <header><h1>SVN Commands for Review</h1></header>


            <section><p>Basic SVN commands:</p>
<ul class="simple">
<li>add, remove, copy, move, mkdir</li>
<li>checkout, commit, update, revert</li>
<li>merge, resolved, diff</li>
<li>status, log</li>
<li>lock, unlock</li>
</ul></section>

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            <header><h1>Presenter Notes</h1></header>
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            <header><h1>Basic Mercurial Commands</h1></header>


            <section><p>Mercurial (hg) vs SVN commands:</p>
<ul class="simple">
<li>add, remove, copy, move, <span class="strike">mkdir</span></li>
<li><span class="strike">checkout</span>, commit, update, revert</li>
<li>merge, resolve, diff, <strong>heads</strong></li>
<li>status, log</li>
<li><span class="strike">lock, unlock</span></li>
</ul>
<p>Additional &quot;distributed commands&quot;:</p>
<ul class="simple">
<li><strong>clone</strong>, <strong>push</strong>, <strong>pull</strong></li>
<li><strong>incoming</strong>, <strong>outgoing</strong></li>
</ul>
<p><strong>Not a whole lot to learn above SVN</strong></p></section>

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            <header><h1>References</h1></header>


            <section><ul class="simple">
<li>Mercurial <a class="reference external" href="http://mercurial.selenic.com/">http://mercurial.selenic.com/</a></li>
<li>Mercurial Wiki <a class="reference external" href="http://mercurial.selenic.com/wiki/">http://mercurial.selenic.com/wiki/</a></li>
<li>Mercurial Book (free!) <a class="reference external" href="http://hgbook.red-bean.com/">http://hgbook.red-bean.com/</a></li>
<li>Hg Init: A Mercurial Tutorial <a class="reference external" href="http://hginit.com">http://hginit.com</a></li>
<li>Version Control By Example (free!) <a class="reference external" href="http://www.ericsink.com/vcbe/">http://www.ericsink.com/vcbe/</a></li>
</ul>
<p>This presentation is available at:</p>
<pre class="literal-block">
$ hg clone https://bitbucket.org/bgneal/dvcs_intro_brownbag
</pre></section>

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            <header><h1>Questions?</h1></header>


          </div>
          <div class="presenter_notes">
            <header><h1>Presenter Notes</h1></header>
            <section>

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  </div>

  <div id="toc" class="sidebar hidden">
    <h2>Table of Contents</h2>
    <table>
      <caption>Table of Contents</caption>

      <tr id="toc-row-1">
        <th><a href="#slide1">Introduction to Distributed Version Control with Mercurial</a></th>
        <td><a href="#slide1">1</a></td>
      </tr>


      <tr id="toc-row-2">
        <th><a href="#slide2">Agenda</a></th>
        <td><a href="#slide2">2</a></td>
      </tr>


      <tr id="toc-row-3">
        <th><a href="#slide3"># whoami</a></th>
        <td><a href="#slide3">3</a></td>
      </tr>


      <tr id="toc-row-4">
        <th><a href="#slide4">Disclaimers</a></th>
        <td><a href="#slide4">4</a></td>
      </tr>


      <tr id="toc-row-5">
        <th><a href="#slide5">Why learn about DVCS?</a></th>
        <td><a href="#slide5">5</a></td>
      </tr>


      <tr id="toc-row-6">
        <th><a href="#slide6">Brief History of Version Control Tools</a></th>
        <td><a href="#slide6">6</a></td>
      </tr>


      <tr id="toc-row-7">
        <th><a href="#slide7">Brief History of Version Control Tools</a></th>
        <td><a href="#slide7">7</a></td>
      </tr>


      <tr id="toc-row-8">
        <th><a href="#slide8">Brief History of Version Control Tools</a></th>
        <td><a href="#slide8">8</a></td>
      </tr>


      <tr id="toc-row-9">
        <th><a href="#slide9">What is a CVCS Again?</a></th>
        <td><a href="#slide9">9</a></td>
      </tr>


      <tr id="toc-row-10">
        <th><a href="#slide10">So what's a DVCS look like?</a></th>
        <td><a href="#slide10">10</a></td>
      </tr>


      <tr id="toc-row-11">
        <th><a href="#slide11">What does a DVCS buy you?</a></th>
        <td><a href="#slide11">11</a></td>
      </tr>


      <tr id="toc-row-12">
        <th><a href="#slide12">Private Workspaces</a></th>
        <td><a href="#slide12">12</a></td>
      </tr>


      <tr id="toc-row-13">
        <th><a href="#slide13">Offline Mode</a></th>
        <td><a href="#slide13">13</a></td>
      </tr>


      <tr id="toc-row-14">
        <th><a href="#slide14">Speed</a></th>
        <td><a href="#slide14">14</a></td>
      </tr>


      <tr id="toc-row-15">
        <th><a href="#slide15">Scalability</a></th>
        <td><a href="#slide15">15</a></td>
      </tr>


      <tr id="toc-row-16">
        <th><a href="#slide16">Split Geography</a></th>
        <td><a href="#slide16">16</a></td>
      </tr>


      <tr id="toc-row-17">
        <th><a href="#slide17">Flexible Workflows</a></th>
        <td><a href="#slide17">17</a></td>
      </tr>


      <tr id="toc-row-18">
        <th><a href="#slide18">Distributed Backups</a></th>
        <td><a href="#slide18">18</a></td>
      </tr>


      <tr id="toc-row-19">
        <th><a href="#slide19">Easier Merging</a></th>
        <td><a href="#slide19">19</a></td>
      </tr>


      <tr id="toc-row-20">
        <th><a href="#slide20">Easier Merging (cont.)</a></th>
        <td><a href="#slide20">20</a></td>
      </tr>


      <tr id="toc-row-21">
        <th><a href="#slide21">Commit Before Merge</a></th>
        <td><a href="#slide21">21</a></td>
      </tr>


      <tr id="toc-row-22">
        <th><a href="#slide22">Okay, what's the catch?</a></th>
        <td><a href="#slide22">22</a></td>
      </tr>


      <tr id="toc-row-23">
        <th><a href="#slide23">Introduction to Mercurial</a></th>
        <td><a href="#slide23">23</a></td>
      </tr>


      <tr id="toc-row-24">
        <th><a href="#slide24">Mercurial Overview</a></th>
        <td><a href="#slide24">24</a></td>
      </tr>


      <tr id="toc-row-25">
        <th><a href="#slide25">Repositories &amp; Working Directories</a></th>
        <td><a href="#slide25">25</a></td>
      </tr>


      <tr id="toc-row-26">
        <th><a href="#slide26">What's in a Repository?</a></th>
        <td><a href="#slide26">26</a></td>
      </tr>


      <tr id="toc-row-27">
        <th><a href="#slide27">What's a Changeset?</a></th>
        <td><a href="#slide27">27</a></td>
      </tr>


      <tr id="toc-row-28">
        <th><a href="#slide28">Branches &amp; Tags</a></th>
        <td><a href="#slide28">28</a></td>
      </tr>


      <tr id="toc-row-29">
        <th><a href="#slide29">A note on branching...</a></th>
        <td><a href="#slide29">29</a></td>
      </tr>


      <tr id="toc-row-30">
        <th><a href="#slide30">Ways to Branch in Hg</a></th>
        <td><a href="#slide30">30</a></td>
      </tr>


      <tr id="toc-row-31">
        <th><a href="#slide31">Example Workflow</a></th>
        <td><a href="#slide31">31</a></td>
      </tr>


      <tr id="toc-row-32">
        <th><a href="#slide32">Example Workflow (cont.)</a></th>
        <td><a href="#slide32">32</a></td>
      </tr>


      <tr id="toc-row-33">
        <th><a href="#slide33">Example Workflow (cont.)</a></th>
        <td><a href="#slide33">33</a></td>
      </tr>


      <tr id="toc-row-34">
        <th><a href="#slide34">SVN Commands for Review</a></th>
        <td><a href="#slide34">34</a></td>
      </tr>


      <tr id="toc-row-35">
        <th><a href="#slide35">Basic Mercurial Commands</a></th>
        <td><a href="#slide35">35</a></td>
      </tr>


      <tr id="toc-row-36">
        <th><a href="#slide36">References</a></th>
        <td><a href="#slide36">36</a></td>
      </tr>


      <tr id="toc-row-37">
        <th><a href="#slide37">Questions?</a></th>
        <td><a href="#slide37">37</a></td>
      </tr>


    </table>
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author	Brian Neal <bgneal@gmail.com>
date	Mon, 25 Jun 2012 19:51:34 -0500
parents	3547bba86af2
children