docs/topics/impala_perf_testing.xml

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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="performance_testing">

  <title>Testing Impala Performance</title>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="Performance"/>
      <data name="Category" value="Troubleshooting"/>
      <data name="Category" value="Proof of Concept"/>
      <data name="Category" value="Logs"/>
      <data name="Category" value="Administrators"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Data Analysts"/>
      <!-- Should reorg this topic to use nested topics, not sections. Some keywords like 'logs' buried in section titles. -->
      <data name="Category" value="Sectionated Pages"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      Test to ensure that Impala is configured for optimal performance. If you have installed Impala with cluster
      management software, complete the processes described in this topic to help ensure a proper
      configuration. These procedures can be used to verify that Impala is set up correctly.
    </p>

    <section id="checking_config_performance">

      <title>Checking Impala Configuration Values</title>

      <p>
        You can inspect Impala configuration values by connecting to your Impala server using a browser.
      </p>

      <p>
        <b>To check Impala configuration values:</b>
      </p>

      <ol>
        <li>
          Use a browser to connect to one of the hosts running <codeph>impalad</codeph> in your environment.
          Connect using an address of the form
          <codeph>http://<varname>hostname</varname>:<varname>port</varname>/varz</codeph>.
          <note>
            In the preceding example, replace <codeph>hostname</codeph> and <codeph>port</codeph> with the name and
            port of your Impala server. The default port is 25000.
          </note>
        </li>

        <li>
          Review the configured values.
          <p>
            For example, to check that your system is configured to use block locality tracking information, you
            would check that the value for <codeph>dfs.datanode.hdfs-blocks-metadata.enabled</codeph> is
            <codeph>true</codeph>.
          </p>
        </li>
      </ol>

      <p id="p_31">
        <b>To check data locality:</b>
      </p>

      <ol>
        <li>
          Execute a query on a dataset that is available across multiple nodes. For example, for a table named
          <codeph>MyTable</codeph> that has a reasonable chance of being spread across multiple DataNodes:
<codeblock>[impalad-host:21000] &gt; SELECT COUNT (*) FROM MyTable</codeblock>
        </li>

        <li>
          After the query completes, review the contents of the Impala logs. You should find a recent message
          similar to the following:
<codeblock>Total remote scan volume = 0</codeblock>
        </li>
      </ol>

      <p>
        The presence of remote scans may indicate <codeph>impalad</codeph> is not running on the correct nodes.
        This can be because some DataNodes do not have <codeph>impalad</codeph> running or it can be because the
        <codeph>impalad</codeph> instance that is starting the query is unable to contact one or more of the
        <codeph>impalad</codeph> instances.
      </p>

      <p>
        <b>To understand the causes of this issue:</b>
      </p>

      <ol>
        <li>
          Connect to the debugging web server. By default, this server runs on port 25000. This page lists all
          <codeph>impalad</codeph> instances running in your cluster. If there are fewer instances than you expect,
          this often indicates some DataNodes are not running <codeph>impalad</codeph>. Ensure
          <codeph>impalad</codeph> is started on all DataNodes.
        </li>

        <li>
          <!-- To do:
            There are other references to this tip about the "Impala daemon's hostname" elsewhere. Could reconcile, conref, or link.
          -->
          If you are using multi-homed hosts, ensure that the Impala daemon's hostname resolves to the interface on
          which <codeph>impalad</codeph> is running. The hostname Impala is using is displayed when
          <codeph>impalad</codeph> starts. To explicitly set the hostname, use the <codeph>--hostname</codeph> flag.
        </li>

        <li>
          Check that <codeph>statestored</codeph> is running as expected. Review the contents of the state store
          log to ensure all instances of <codeph>impalad</codeph> are listed as having connected to the state
          store.
        </li>
      </ol>
    </section>

    <section id="checking_config_logs">

      <title>Reviewing Impala Logs</title>

      <p>
        You can review the contents of the Impala logs for signs that short-circuit reads or block location
        tracking are not functioning. Before checking logs, execute a simple query against a small HDFS dataset.
        Completing a query task generates log messages using current settings. Information on starting Impala and
        executing queries can be found in <xref href="impala_processes.xml#processes"/> and
        <xref href="impala_impala_shell.xml#impala_shell"/>. Information on logging can be found in
        <xref href="impala_logging.xml#logging"/>. Log messages and their interpretations are as follows:
      </p>

      <table>
        <tgroup cols="2">
          <colspec colname="1" colwidth="30*"/>
          <colspec colname="2" colwidth="10*"/>
          <thead>
            <row>
              <entry>
                Log Message
              </entry>
              <entry>
                Interpretation
              </entry>
            </row>
          </thead>
          <tbody>
            <row>
              <entry>
                <p>
<pre>Unknown disk id. This will negatively affect performance. Check your hdfs settings to enable block location metadata
</pre>
                </p>
              </entry>
              <entry>
                <p>
                  Tracking block locality is not enabled.
                </p>
              </entry>
            </row>
            <row>
              <entry>
                <p>
<pre>Unable to load native-hadoop library for your platform... using builtin-java classes where applicable</pre>
                </p>
              </entry>
              <entry>
                <p>
                  Native checksumming is not enabled.
                </p>
              </entry>
            </row>
          </tbody>
        </tgroup>
      </table>
    </section>
  </conbody>
</concept>