docs/topics/impala_prereqs.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="prereqs">

  <title>Impala Requirements</title>
  <titlealts audience="PDF"><navtitle>Requirements</navtitle></titlealts>

  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="Requirements"/>
      <data name="Category" value="Planning"/>
      <data name="Category" value="Installing"/>
      <data name="Category" value="Upgrading"/>
      <data name="Category" value="Administrators"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Data Analysts"/>
      <!-- Another instance of a topic pulled into the map twice, resulting in a second HTML page with a *1.html filename. -->
      <data name="Category" value="Duplicate Topics"/>
      <!-- Using a separate category, 'Multimap', to flag those pages that are duplicate because of multiple DITA map references. -->
      <data name="Category" value="Multimap"/>
    </metadata>
  </prolog>

  <conbody>

    <p>
      <indexterm audience="hidden">prerequisites</indexterm>
      <indexterm audience="hidden">requirements</indexterm>
      To perform as expected, Impala depends on the availability of the software, hardware, and configurations
      described in the following sections.
    </p>

    <p outputclass="toc inpage"/>
  </conbody>

  <concept id="prereqs_os">

    <title>Supported Operating Systems</title>

    <conbody>

      <p>
        <indexterm audience="hidden">software requirements</indexterm>
        <indexterm audience="hidden">Red Hat Enterprise Linux</indexterm>
        <indexterm audience="hidden">RHEL</indexterm>
        <indexterm audience="hidden">CentOS</indexterm>
        <indexterm audience="hidden">SLES</indexterm>
        <indexterm audience="hidden">Ubuntu</indexterm>
        <indexterm audience="hidden">SUSE</indexterm>
        <indexterm audience="hidden">Debian</indexterm>
        Apache Impala runs on Linux systems only. See the <filepath>README.md</filepath>
        file for more information.
      </p>
    </conbody>
  </concept>

  <concept id="prereqs_hive">

    <title>Hive Metastore and Related Configuration</title>
  <prolog>
    <metadata>
      <data name="Category" value="Metastore"/>
      <data name="Category" value="Hive"/>
    </metadata>
  </prolog>

    <conbody>

      <p>
        <indexterm audience="hidden">Hive</indexterm>
        <indexterm audience="hidden">MySQL</indexterm>
        <indexterm audience="hidden">PostgreSQL</indexterm>
        Impala can interoperate with data stored in Hive, and uses the same infrastructure as Hive for tracking
        metadata about schema objects such as tables and columns. The following components are prerequisites for
        Impala:
      </p>

      <ul>
        <li>
          MySQL or PostgreSQL, to act as a metastore database for both Impala and Hive.
          <note>
            <p>
              Installing and configuring a Hive metastore is an Impala requirement. Impala does not work without
              the metastore database. For the process of installing and configuring the metastore, see
              <xref href="impala_install.xml#install"/>.
            </p>

            <p>
              Always configure a <b>Hive metastore service</b> rather than connecting directly to the metastore
              database. The Hive metastore service is required to interoperate between different levels of
              metastore APIs if this is necessary for your environment, and using it avoids known issues with
              connecting directly to the metastore database.
            </p>

            <p>
              A summary of the metastore installation process is as follows:
            </p>
            <ul>
              <li>
                Install a MySQL or PostgreSQL database. Start the database if it is not started after installation.
              </li>

              <li>
                Download the
                <xref href="http://www.mysql.com/products/connector/" scope="external" format="html">MySQL
                connector</xref> or the
                <xref href="http://jdbc.postgresql.org/download.html" scope="external" format="html">PostgreSQL
                connector</xref> and place it in the <codeph>/usr/share/java/</codeph> directory.
              </li>

              <li>
                Use the appropriate command line tool for your database to create the metastore database.
              </li>

              <li>
                Use the appropriate command line tool for your database to grant privileges for the metastore
                database to the <codeph>hive</codeph> user.
              </li>

              <li>
                Modify <codeph>hive-site.xml</codeph> to include information matching your particular database: its
                URL, username, and password. You will copy the <codeph>hive-site.xml</codeph> file to the Impala
                Configuration Directory later in the Impala installation process.
              </li>
            </ul>
          </note>
        </li>

        <li>
          <b>Optional:</b> Hive. Although only the Hive metastore database is required for Impala to function, you
          might install Hive on some client machines to create and load data into tables that use certain file
          formats. See <xref href="impala_file_formats.xml#file_formats"/> for details. Hive does not need to be
          installed on the same DataNodes as Impala; it just needs access to the same metastore database.
        </li>
      </ul>
    </conbody>
  </concept>

  <concept id="prereqs_java">

    <title>Java Dependencies</title>
  <prolog>
    <metadata>
      <data name="Category" value="Java"/>
    </metadata>
  </prolog>

    <conbody>

      <p>
        <indexterm audience="hidden">Java</indexterm>
        <indexterm audience="hidden">impala-dependencies.jar</indexterm>
        Although Impala is primarily written in C++, it does use Java to communicate with various Hadoop
        components:
      </p>

      <ul>
        <li>
          The officially supported JVM for Impala is the Oracle JVM. Other JVMs might cause issues, typically
          resulting in a failure at <cmdname>impalad</cmdname> startup. In particular, the JamVM used by default on
          certain levels of Ubuntu systems can cause <cmdname>impalad</cmdname> to fail to start.
        </li>

        <li>
          Internally, the <cmdname>impalad</cmdname> daemon relies on the <codeph>JAVA_HOME</codeph> environment
          variable to locate the system Java libraries. Make sure the <cmdname>impalad</cmdname> service is not run
          from an environment with an incorrect setting for this variable.
        </li>

        <li>
          All Java dependencies are packaged in the <codeph>impala-dependencies.jar</codeph> file, which is located
          at <codeph>/usr/lib/impala/lib/</codeph>. These map to everything that is built under
          <codeph>fe/target/dependency</codeph>.
        </li>
      </ul>
    </conbody>
  </concept>

  <concept id="prereqs_network">

    <title>Networking Configuration Requirements</title>
  <prolog>
    <metadata>
      <data name="Category" value="Network"/>
    </metadata>
  </prolog>

    <conbody>

      <p>
        <indexterm audience="hidden">network configuration</indexterm>
        As part of ensuring best performance, Impala attempts to complete tasks on local data, as opposed to using
        network connections to work with remote data. To support this goal, Impala matches
        the <b>hostname</b> provided to each Impala daemon with the <b>IP address</b> of each DataNode by
        resolving the hostname flag to an IP address. For Impala to work with local data, use a single IP interface
        for the DataNode and the Impala daemon on each machine. Ensure that the Impala daemon's hostname flag
        resolves to the IP address of the DataNode. For single-homed machines, this is usually automatic, but for
        multi-homed machines, ensure that the Impala daemon's hostname resolves to the correct interface. Impala
        tries to detect the correct hostname at start-up, and prints the derived hostname at the start of the log
        in a message of the form:
      </p>

<codeblock>Using hostname: impala-daemon-1.example.com</codeblock>

      <p>
        In the majority of cases, this automatic detection works correctly. If you need to explicitly set the
        hostname, do so by setting the <codeph>--hostname</codeph> flag.
      </p>
    </conbody>
  </concept>

  <concept id="prereqs_hardware">

    <title>Hardware Requirements</title>

    <conbody>

      <p>
        <indexterm audience="hidden">hardware requirements</indexterm>
        <indexterm audience="hidden">capacity</indexterm>
        <indexterm audience="hidden">RAM</indexterm>
        <indexterm audience="hidden">memory</indexterm>
        <indexterm audience="hidden">CPU</indexterm>
        <indexterm audience="hidden">processor</indexterm>
        <indexterm audience="hidden">Intel</indexterm>
        <indexterm audience="hidden">AMD</indexterm>
        During join operations, portions of data from each joined table are loaded into memory. Data sets can be
        very large, so ensure your hardware has sufficient memory to accommodate the joins you anticipate
        completing.
      </p>

      <p>
        While requirements vary according to data set size, the following is generally recommended:
      </p>

      <ul>
        <li rev="2.0.0">
          CPU - Impala version 2.2 and higher uses the SSSE3 instruction set, which is included in newer processors.
          <note>
            This required level of processor is the same as in Impala version 1.x. The Impala 2.0 and 2.1 releases
            had a stricter requirement for the SSE4.1 instruction set, which has now been relaxed.
          </note>
<!--
          For best performance use:
          <ul>
            <li>
              Intel - Nehalem (released 2008) or later processors.
            </li>

            <li>
              AMD - Bulldozer (released 2011) or later processors.
            </li>
          </ul>
-->
        </li>

        <li rev="1.2">
          Memory - 128 GB or more recommended, ideally 256 GB or more. If the intermediate results during query
          processing on a particular node exceed the amount of memory available to Impala on that node, the query
          writes temporary work data to disk, which can lead to long query times. Note that because the work is
          parallelized, and intermediate results for aggregate queries are typically smaller than the original
          data, Impala can query and join tables that are much larger than the memory available on an individual
          node.
        </li>

        <li>
          Storage - DataNodes with 12 or more disks each. I/O speeds are often the limiting factor for disk
          performance with Impala. Ensure that you have sufficient disk space to store the data Impala will be
          querying.
        </li>
      </ul>
    </conbody>
  </concept>

  <concept id="prereqs_account">

    <title>User Account Requirements</title>
  <prolog>
    <metadata>
      <data name="Category" value="Users"/>
    </metadata>
  </prolog>

    <conbody>

      <p>
        <indexterm audience="hidden">impala user</indexterm>
        <indexterm audience="hidden">impala group</indexterm>
        <indexterm audience="hidden">root user</indexterm>
        Impala creates and uses a user and group named <codeph>impala</codeph>. Do not delete this account or group
        and do not modify the account's or group's permissions and rights. Ensure no existing systems obstruct the
        functioning of these accounts and groups. For example, if you have scripts that delete user accounts not in
        a white-list, add these accounts to the list of permitted accounts.
      </p>

      <p>
        For correct file deletion during <codeph>DROP TABLE</codeph> operations, Impala must be able to move files
        to the HDFS trashcan. You might need to create an HDFS directory <filepath>/user/impala</filepath>,
        writeable by the <codeph>impala</codeph> user, so that the trashcan can be created. Otherwise, data files
        might remain behind after a <codeph>DROP TABLE</codeph> statement.
      </p>

      <p>
        Impala should not run as root. Best Impala performance is achieved using direct reads, but root is not
        permitted to use direct reads. Therefore, running Impala as root negatively affects performance.
      </p>

      <p>
        By default, any user can connect to Impala and access all the associated databases and tables. You can
        enable authorization and authentication based on the Linux OS user who connects to the Impala server, and
        the associated groups for that user. <xref href="impala_security.xml#security"/> for details. These
        security features do not change the underlying file permission requirements; the <codeph>impala</codeph>
        user still needs to be able to access the data files.
      </p>
    </conbody>
  </concept>
</concept>