episode-5.xml

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<item xmlns:itunes="http://www.itunes.com/dtds/podcast-1.0.dtd">
  <title>nlog</title>
  <guests>Teemu Koponen from Styra and Yusheng Wang from VMware</guests>
  <description>
    <p>
      Interview with Teemu Koponen of <a href="http://www.styra.com/">Styra</a>
      and Yusheng Wang of <a href="http://www.vmware.com/">VMware</a>, about
      the nlog language.
    </p>

    <p>
      nlog, in this context, is unrelated to the logging platform for .NET.  It
      is a database language, a simplified form of <a
      href="https://en.wikipedia.org/wiki/Datalog">Datalog</a> that lacks
      recursion and negation.  Teemu designed this language for use in Nicira
      NVP, the forerunner of <a
      href="https://www.sdxcentral.com/resources/vmware/what-is-vmware-nsx/">VMware
      NSX-MH</a>.  Yusheng is now working to implement nlog in <a
      href="https://networkheresy.com/2015/01/13/ovn-bringing-native-virtual-networking-to-ovs/">OVN</a>.
    </p>

    <p>
      Teemu and Yusheng begin by describing the nlog language, its name (the
      ``N'' stands for ``Nicira.''), and its purpose and contrast it with more
      commonly known languages such as SQL.  An nlog (or Datalog) program
      consists of a series of queries against input table that produce new
      tables, which can be reused in subsequent queries to eventually produce
      output tables.
    </p>

    <p>
      In a network virtualization system such as NVP or OVN, input tables
      contain information on the configuration or the state of the system.  The
      queries transform this input into flow tables to push down to switches.
      The nlog program acts a function of the entire contents of the input
      tables, without reference to a concept of time or order.  This simplifies
      implementation, because it avoids ordering problems found so pervasively
      in distributed systems.  Thus, versus hand-code state machines, nlog
      offers better hope of correctness and easier quality assurance, since it
      allows programmers to specify the desired results rather than all of the
      possible state transitions that could lead there.
    </p>

    <p>
      Topics include:
    </p>

    <ul>
      <li>
        Related (more complicated) work in academia.
      </li>

      <li>
        External functions for mapping output.
      </li>

      <li>
        Query planning in NVP and in OVN.
      </li>

      <li>
        Sharding, threading, and performance.
      </li>

      <li>
        Where Yusheng is planning to first propose nlog for use in OVN.
      </li>
      
      <li>
        The simple Java-based network virtualization system that Yusheng built
        to demonstrate the idea.
      </li>

      <li>
        The patches that we should expect to see soon from Yusheng.
      </li>

      <li>
        Code size for nlog implementations (small!).
      </li>

      <li>
        Strategies for testing an nlog implementation.
      </li>

      <li>
        Data types in nlog, and risks of asynchronous interfacing
      </li>

      <li>
        Convergence, performance, and transactions.
      </li>

      <li>
        Lessons learned:

        <ol>
          <li>
            Only implement a DSL if you know what you're getting in for.
          </li>

          <li>
            nlog solved correctness issues, period (leaving developers to worry
            about scale).
          </li>
        </ol>
      </li>
    </ul>

    <p>
      You can reach Teemu at <a
      href="mailto:koponen@styra.com">koponen@styra.com</a> and Yusheng at <a
      href="mailto:yshwang@vmware.com">yshwang@vmware.com</a>.
    </p>

    <p class="attribution">
      OVS Orbit is produced by <a href="mailto:blp@ovn.org">Ben Pfaff</a>.  The
      intro and bumper music is <a
      href="http://dig.ccmixter.org/files/myfreemickey/48180">Electro
      Deluxe</a>, featuring Gurdonack, copyright 2014 by My Free Mickey.  The
      outro music is <a
      href="http://dig.ccmixter.org/files/JeffSpeed68/44932">Girls like
      you</a>, featuring Thespinwires, copyright 2014 by Stefan Kartenberg.
      All content is licensed under a Creative Commons <a
      href="http://creativecommons.org/licenses/by/3.0/">Attribution 3.0
      Unported (CC BY 3.0)</a> license.
    </p>
  </description>
<pubDate>Thu, 26 May 2016 01:05:53 GMT</pubDate>
</item>