impala/docs/topics/impala_perf_testing.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
-->
<!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 without
      Cloudera Manager, complete the processes described in this topic to help ensure a proper configuration. Even
      if you installed Impala with Cloudera Manager, which automatically applies appropriate configurations, 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>