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 <div class="section">
  <div class="titlepage">
   <div>
    <div>
     <h2 class="title">
      <a name="faqs-mysql-cluster">
      </a>
      A.10 MySQL 8.4 FAQ: NDB Cluster
     </h2>
    </div>
   </div>
  </div>
  <a class="indexterm" name="idm46045056063952">
  </a>
  <a class="indexterm" name="idm46045056062480">
  </a>
  <a class="indexterm" name="idm46045056061024">
  </a>
  <p>
   In the following section, we answer questions that are frequently
      asked about MySQL NDB Cluster and the
   <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
    <code class="literal">
     NDB
    </code>
   </a>
   storage engine.
  </p>
  <div class="qandaset">
   <a name="idm46045056057808">
   </a>
   <dl>
    <dt>
     A.10.1.
     <a href="faqs-mysql-cluster.html#faq-cluster-which-versions-support-cluster">
      Which versions of the MySQL software support NDB Cluster? Do I
        have to compile from source?
     </a>
    </dt>
    <dt>
     A.10.2.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-is-ndb">
      What do “NDB” and “NDBCLUSTER” mean?
     </a>
    </dt>
    <dt>
     A.10.3.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-cluster-vs-replication">
      What is the difference between using NDB Cluster versus using
        MySQL Replication?
     </a>
    </dt>
    <dt>
     A.10.4.
     <a href="faqs-mysql-cluster.html#faq-cluster-how-cluster-network-need">
      Do I need any special networking to run NDB Cluster? How do
        computers in a cluster communicate?
     </a>
    </dt>
    <dt>
     A.10.5.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-min-hosts-cluster">
      How many computers do I need to run an NDB Cluster, and why?
     </a>
    </dt>
    <dt>
     A.10.6.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-hosts-do-clustering">
      What do the different computers do in an NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.7.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-show-nodegroup-star">
      When I run the SHOW command in the NDB
        Cluster management client, I see a line of output that looks
        like this:
     </a>
    </dt>
    <dt>
     A.10.8.
     <a href="faqs-mysql-cluster.html#faq-cluster-which-os-clustering">
      With which operating systems can I use NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.9.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-cluster-requirements">
      What are the hardware requirements for running NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.10.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-memory-needed-cluster">
      How much RAM do I need to use NDB Cluster? Is it possible to use
        disk memory at all?
     </a>
    </dt>
    <dt>
     A.10.11.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-cluster-file-systems">
      What file systems can I use with NDB Cluster? What about network
        file systems or network shares?
     </a>
    </dt>
    <dt>
     A.10.12.
     <a href="faqs-mysql-cluster.html#faq-cluster-can-cluster-vm">
      Can I run NDB Cluster nodes inside virtual machines (such as
        those created by VMWare, VirtualBox, Parallels, or Xen)?
     </a>
    </dt>
    <dt>
     A.10.13.
     <a href="faqs-mysql-cluster.html#faq-cluster-why-error-1114">
      I am trying to populate an NDB Cluster database. The loading
        process terminates prematurely and I get an error message like
        this one:
     </a>
    </dt>
    <dt>
     A.10.14.
     <a href="faqs-mysql-cluster.html#faq-cluster-can-cluster-remote-network">
      NDB Cluster uses TCP/IP. Does this mean that I can run it over
        the Internet, with one or more nodes in remote locations?
     </a>
    </dt>
    <dt>
     A.10.15.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-language-needed-cluster">
      Do I have to learn a new programming or query language to use
        NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.16.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-api-cluster-support">
      What programming languages and APIs are supported by NDB
        Cluster?
     </a>
    </dt>
    <dt>
     A.10.17.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-cluster-management-tools">
      Does NDB Cluster include any management tools?
     </a>
    </dt>
    <dt>
     A.10.18.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-cluster-errors-are">
      How do I find out what an error or warning message means when
        using NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.19.
     <a href="faqs-mysql-cluster.html#faq-cluster-is-cluster-transaction-safe">
      Is NDB Cluster transaction-safe? What isolation levels are
        supported?
     </a>
    </dt>
    <dt>
     A.10.20.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-storage-engines-cluster">
      What storage engines are supported by NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.21.
     <a href="faqs-mysql-cluster.html#faq-cluster-is-data-loss-no-power">
      In the event of a catastrophic failure— for example, the
        whole city loses power and my UPS
        fails—would I lose all my data?
     </a>
    </dt>
    <dt>
     A.10.22.
     <a href="faqs-mysql-cluster.html#faq-cluster-can-cluster-fullindex">
      Is it possible to use FULLTEXT indexes with
        NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.23.
     <a href="faqs-mysql-cluster.html#faq-cluster-can-multinode-cluster-one-host">
      Can I run multiple nodes on a single computer?
     </a>
    </dt>
    <dt>
     A.10.24.
     <a href="faqs-mysql-cluster.html#faq-cluster-how-add-nodes-no-restart">
      Can I add data nodes to an NDB Cluster without restarting it?
     </a>
    </dt>
    <dt>
     A.10.25.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-cluster-limitations">
      Are there any limitations that I should be aware of when using
        NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.26.
     <a href="faqs-mysql-cluster.html#faq-cluster-have-foreign-keys-cluster">
      Does NDB Cluster support foreign keys?
     </a>
    </dt>
    <dt>
     A.10.27.
     <a href="faqs-mysql-cluster.html#faq-cluster-how-import-db-cluster">
      How do I import an existing MySQL database into an NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.28.
     <a href="faqs-mysql-cluster.html#faq-cluster-how-nodes-communicate">
      How do NDB Cluster nodes communicate with one another?
     </a>
    </dt>
    <dt>
     A.10.29.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-is-arbitrator">
      What is an arbitrator?
     </a>
    </dt>
    <dt>
     A.10.30.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-types-cluster-support">
      What data types are supported by NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.31.
     <a href="faqs-mysql-cluster.html#faq-cluster-how-start-stop-cluster">
      How do I start and stop NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.32.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-shutdown-do-data">
      What happens to NDB Cluster data when the cluster is shut down?
     </a>
    </dt>
    <dt>
     A.10.33.
     <a href="faqs-mysql-cluster.html#faq-cluster-have-multiple-node-managers">
      Is it a good idea to have more than one management node for an
        NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.34.
     <a href="faqs-mysql-cluster.html#faq-cluster-have-different-cluster-hosts">
      Can I mix different kinds of hardware and operating systems in
        one NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.35.
     <a href="faqs-mysql-cluster.html#faq-cluster-have-multiple-nodes-one-host">
      Can I run two data nodes on a single host? Two SQL nodes?
     </a>
    </dt>
    <dt>
     A.10.36.
     <a href="faqs-mysql-cluster.html#faq-cluster-have-host-names-cluster">
      Can I use host names with NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.37.
     <a href="faqs-mysql-cluster.html#faq-cluster-have-ipv6-support-cluster">
      Does NDB Cluster support IPv6?
     </a>
    </dt>
    <dt>
     A.10.38.
     <a href="faqs-mysql-cluster.html#faq-cluster-have-multiple-users-servers-cluster">
      How do I handle MySQL users in an NDB Cluster having multiple
        MySQL servers?
     </a>
    </dt>
    <dt>
     A.10.39.
     <a href="faqs-mysql-cluster.html#faq-cluster-how-continue-after-node-error">
      How do I continue to send queries in the event that one of the
        SQL nodes fails?
     </a>
    </dt>
    <dt>
     A.10.40.
     <a href="faqs-mysql-cluster.html#faq-cluster-how-backup-restore-cluster">
      How do I back up and restore an NDB Cluster?
     </a>
    </dt>
    <dt>
     A.10.41.
     <a href="faqs-mysql-cluster.html#faq-cluster-what-angel-process">
      What is an “angel process”?
     </a>
    </dt>
   </dl>
   <table border="0" style="width: 100%;">
    <colgroup>
     <col align="left" width="1%"/>
     <col/>
    </colgroup>
    <tbody>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-which-versions-support-cluster">
       </a>
       <a name="idm46045056057008">
       </a>
       <p>
        <b>
         A.10.1.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Which versions of the MySQL software support NDB Cluster? Do I
        have to compile from source?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster is not supported in standard MySQL Server releases.
        Instead, MySQL NDB Cluster is provided as a separate product.
        Available NDB Cluster release series include the following:
       </p>
       <div class="itemizedlist">
        <ul class="itemizedlist" style="list-style-type: disc; ">
         <li class="listitem">
          <p>
           <b>
            NDB Cluster 7.3 / NDB Cluster 7.4.
           </b>
           These two series are no longer maintained or supported for
              new deployments. Users of NDB Cluster 7.3 or 7.4 should
              upgrade to NDB 7.5 or newer as soon as possible. We
              recommend that new deployments use the latest NDB Cluster
              8.0 release.
          </p>
         </li>
         <li class="listitem">
          <p>
           <b>
            NDB Cluster 7.5.
           </b>
           This series is a previous General Availability (GA)
              version of NDB Cluster, still available for production
              use, although we recommend that new deployments use the
              latest NDB Cluster 8.0 release. The latest NDB Cluster 7.5
              releases can be obtained from
           <a class="ulink" href="https://dev.mysql.com/downloads/cluster/" target="_top">
            https://dev.mysql.com/downloads/cluster/
           </a>
           .
          </p>
         </li>
         <li class="listitem">
          <p>
           <b>
            NDB Cluster 7.6.
           </b>
           This series is a previous General Availability (GA)
              version of NDB Cluster, still available for production
              use, although we recommend that new deployments use the
              latest NDB Cluster 8.0 release. The latest NDB Cluster 7.6
              releases can be obtained from
           <a class="ulink" href="https://dev.mysql.com/downloads/cluster/" target="_top">
            https://dev.mysql.com/downloads/cluster/
           </a>
           .
          </p>
         </li>
         <li class="listitem">
          <p>
           <b>
            NDB Cluster 8.0.
           </b>
           This series is the most recent General Availability (GA)
              version of NDB Cluster, based on version 8.0 of the
           <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
            <code class="literal">
             NDB
            </code>
           </a>
           storage engine and MySQL
              Server 8.0. NDB Cluster 8.0 is available for production
              use; new deployments intended for production should use
              the latest GA release in this series, which is currently
              NDB Cluster 8.0.41. You can obtain the
              most recent NDB Cluster 8.0 release from
           <a class="ulink" href="https://dev.mysql.com/downloads/cluster/" target="_top">
            https://dev.mysql.com/downloads/cluster/
           </a>
           . For
              information about new features and other important changes
              in this series, see
           <a class="ulink" href="/doc/refman/8.0/en/mysql-cluster-what-is-new.html" target="_top">
            What is New in MySQL NDB Cluster 8.0
           </a>
           .
          </p>
         </li>
        </ul>
       </div>
       <p>
        You can obtain and compile NDB Cluster from source (see
        <a class="xref" href="mysql-cluster-install-linux-source.html" title="25.3.1.4 Building NDB Cluster from Source on Linux">
         Section 25.3.1.4, “Building NDB Cluster from Source on Linux”
        </a>
        , and
        <a class="xref" href="mysql-cluster-install-windows-source.html" title="25.3.2.2 Compiling and Installing NDB Cluster from Source on Windows">
         Section 25.3.2.2, “Compiling and Installing NDB Cluster from Source on Windows”
        </a>
        ), but for
        all but the most specialized cases, we recommend using one of
        the following installers provided by Oracle that is appropriate
        to your operating platform and circumstances:
       </p>
       <div class="itemizedlist">
        <ul class="itemizedlist" style="list-style-type: disc; ">
         <li class="listitem">
          <p>
           Linux
           <a class="link" href="mysql-cluster-install-linux-binary.html" title="25.3.1.1 Installing an NDB Cluster Binary Release on Linux">
            binary
            release
           </a>
           (
           <code class="filename">
            tar.gz
           </code>
           file)
          </p>
         </li>
         <li class="listitem">
          <p>
           Linux
           <a class="link" href="mysql-cluster-install-linux-rpm.html" title="25.3.1.2 Installing NDB Cluster from RPM">
            RPM
            package
           </a>
          </p>
         </li>
         <li class="listitem">
          <p>
           Linux
           <a class="link" href="mysql-cluster-install-debian.html" title="25.3.1.3 Installing NDB Cluster Using .deb Files">
            <code class="filename">
             .deb
            </code>
            file
           </a>
          </p>
         </li>
         <li class="listitem">
          <p>
           Windows
           <a class="link" href="mysql-cluster-install-windows-binary.html" title="25.3.2.1 Installing NDB Cluster on Windows from a Binary Release">
            binary
            <span class="quote">
             “
             <span class="quote">
              no-install
             </span>
             ”
            </span>
            release
           </a>
          </p>
         </li>
         <li class="listitem">
          <p>
           Windows
           <a class="ulink" href="/doc/refman/8.0/en/mysql-installer.html" target="_top">
            MSI Installer
           </a>
          </p>
         </li>
        </ul>
       </div>
       <p>
        Installation packages may also be available from your
        platform's package management system.
       </p>
       <p>
        You can determine whether your MySQL Server has
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        support using one of the
        statements
        <code class="literal">
         SHOW VARIABLES LIKE 'have_%'
        </code>
        ,
        <a class="link" href="show-engines.html" title="15.7.7.17 SHOW ENGINES Statement">
         <code class="literal">
          SHOW ENGINES
         </code>
        </a>
        , or
        <a class="link" href="show-plugins.html" title="15.7.7.27 SHOW PLUGINS Statement">
         <code class="literal">
          SHOW PLUGINS
         </code>
        </a>
        .
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-is-ndb">
       </a>
       <a name="idm46045056024704">
       </a>
       <p>
        <b>
         A.10.2.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        What do
        <span class="quote">
         “
         <span class="quote">
          NDB
         </span>
         ”
        </span>
        and
        <span class="quote">
         “
         <span class="quote">
          NDBCLUSTER
         </span>
         ”
        </span>
        mean?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        <span class="quote">
         “
         <span class="quote">
          NDB
         </span>
         ”
        </span>
        stands for
        <span class="quote">
         “
         <span class="quote">
          <span class="bold">
           <strong>
            N
           </strong>
          </span>
          etwork
          <span class="bold">
           <strong>
            D
           </strong>
          </span>
          ata
          <span class="bold">
           <strong>
            b
           </strong>
          </span>
          ase
         </span>
         ”
        </span>
        .
        <code class="literal">
         NDB
        </code>
        and
        <code class="literal">
         NDBCLUSTER
        </code>
        are
        both names for the storage engine that enables clustering
        support with MySQL.
        <code class="literal">
         NDB
        </code>
        is preferred, but
        either name is correct.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-cluster-vs-replication">
       </a>
       <a name="idm46045056017008">
       </a>
       <p>
        <b>
         A.10.3.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        What is the difference between using NDB Cluster versus using
        MySQL Replication?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        In traditional MySQL replication, a source MySQL server updates
        one or more replicas. Transactions are committed sequentially,
        and a slow transaction can cause the replica to lag behind the
        source. This means that if the source fails, it is possible that
        the replica might not have recorded the last few transactions.
        If a transaction-safe engine such as
        <a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
         <code class="literal">
          InnoDB
         </code>
        </a>
        is being used, a transaction
        is either completed on the replica or not applied at all, but
        replication does not guarantee that all data on the source and
        the replica remains consistent at all times. In NDB Cluster, all
        data nodes are kept in synchrony, and a transaction committed by
        any one data node is committed for all data nodes. In the event
        of a data node failure, all remaining data nodes remain in a
        consistent state.
       </p>
       <p>
        In short, whereas standard MySQL replication is
        <span class="firstterm">
         asynchronous
        </span>
        , NDB Cluster
        is
        <span class="firstterm">
         synchronous
        </span>
        .
       </p>
       <p>
        Asynchronous replication is also available in NDB Cluster.
        <span class="firstterm">
         NDB Cluster Replication
        </span>
        (also sometimes known as
        <span class="quote">
         “
         <span class="quote">
          geo-replication
         </span>
         ”
        </span>
        )
        includes the capability to replicate both between two NDB
        Clusters, and from an NDB Cluster to a non-Cluster MySQL server.
        See
        <a class="xref" href="mysql-cluster-replication.html" title="25.7 NDB Cluster Replication">
         Section 25.7, “NDB Cluster Replication”
        </a>
        .
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-how-cluster-network-need">
       </a>
       <a name="idm46045056008384">
       </a>
       <p>
        <b>
         A.10.4.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Do I need any special networking to run NDB Cluster? How do
        computers in a cluster communicate?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster is intended to be used in a high-bandwidth
        environment, with computers connecting using TCP/IP. Its
        performance depends directly upon the connection speed between
        the cluster's computers. The minimum connectivity
        requirements for NDB Cluster include a typical 100-megabit
        Ethernet network or the equivalent. We recommend you use gigabit
        Ethernet whenever available.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-min-hosts-cluster">
       </a>
       <a name="idm46045056005872">
       </a>
       <p>
        <b>
         A.10.5.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        How many computers do I need to run an NDB Cluster, and why?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        A minimum of three computers is required to run a viable
        cluster. However, the minimum
        <span class="emphasis">
         <em>
          recommended
         </em>
        </span>
        number of computers in an NDB Cluster is four: one each to run
        the management and SQL nodes, and two computers to serve as data
        nodes. The purpose of the two data nodes is to provide
        redundancy; the management node must run on a separate machine
        to guarantee continued arbitration services in the event that
        one of the data nodes fails.
       </p>
       <p>
        To provide increased throughput and high availability, you
        should use multiple SQL nodes (MySQL Servers connected to the
        cluster). It is also possible (although not strictly necessary)
        to run multiple management servers.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-hosts-do-clustering">
       </a>
       <a name="idm46045056002304">
       </a>
       <p>
        <b>
         A.10.6.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        What do the different computers do in an NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        An NDB Cluster has both a physical and logical organization,
        with computers being the physical elements. The logical or
        functional elements of a cluster are referred to as
        <span class="firstterm">
         nodes
        </span>
        , and a computer
        housing a cluster node is sometimes referred to as a
        <span class="firstterm">
         cluster host
        </span>
        . There are
        three types of nodes, each corresponding to a specific role
        within the cluster. These are:
       </p>
       <div class="itemizedlist">
        <ul class="itemizedlist" style="list-style-type: disc; ">
         <li class="listitem">
          <p>
           <b>
            Management node.
           </b>
           This node provides management services for the cluster as
              a whole, including startup, shutdown, backups, and
              configuration data for the other nodes. The management
              node server is implemented as the application
           <a class="link" href="mysql-cluster-programs-ndb-mgmd.html" title="25.5.4 ndb_mgmd — The NDB Cluster Management Server Daemon">
            <span class="command">
             <strong>
              ndb_mgmd
             </strong>
            </span>
           </a>
           ; the management client used to
              control NDB Cluster is
           <a class="link" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
            <span class="command">
             <strong>
              ndb_mgm
             </strong>
            </span>
           </a>
           . See
           <a class="xref" href="mysql-cluster-programs-ndb-mgmd.html" title="25.5.4 ndb_mgmd — The NDB Cluster Management Server Daemon">
            Section 25.5.4, “ndb_mgmd — The NDB Cluster Management Server Daemon”
           </a>
           , and
           <a class="xref" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
            Section 25.5.5, “ndb_mgm — The NDB Cluster Management Client”
           </a>
           , for
              information about these programs.
          </p>
         </li>
         <li class="listitem">
          <p>
           <b>
            Data node.
           </b>
           This type of node stores and replicates data. Data node
              functionality is handled by instances of the
           <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
            <code class="literal">
             NDB
            </code>
           </a>
           data node process
           <a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
            <span class="command">
             <strong>
              ndbd
             </strong>
            </span>
           </a>
           . For more information, see
           <a class="xref" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
            Section 25.5.1, “ndbd — The NDB Cluster Data Node Daemon”
           </a>
           .
          </p>
         </li>
         <li class="listitem">
          <p>
           <b>
            SQL node.
           </b>
           This is simply an instance of MySQL Server
              (
           <a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
            <span class="command">
             <strong>
              mysqld
             </strong>
            </span>
           </a>
           ) that is built with support for
              the
           <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
            <code class="literal">
             NDBCLUSTER
            </code>
           </a>
           storage engine
              and started with the
           <code class="option">
            --ndb-cluster
           </code>
           option
              to enable the engine and the
           <code class="option">
            --ndb-connectstring
           </code>
           option to enable it
              to connect to an NDB Cluster management server. For more
              about these options, see
           <a class="xref" href="mysql-cluster-options-variables.html#mysql-cluster-program-options-mysqld" title="25.4.3.9.1 MySQL Server Options for NDB Cluster">
            Section 25.4.3.9.1, “MySQL Server Options for NDB Cluster”
           </a>
           .
          </p>
          <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
           <div class="admon-title">
            Note
           </div>
           <p>
            An
            <span class="firstterm">
             API node
            </span>
            is any
              application that makes direct use of Cluster data nodes
              for data storage and retrieval. An SQL node can thus be
              considered a type of API node that uses a MySQL Server to
              provide an SQL interface to the Cluster. You can write
              such applications (that do not depend on a MySQL Server)
              using the NDB API, which supplies a direct,
              object-oriented transaction and scanning interface to NDB
              Cluster data; see
            <a class="ulink" href="/doc/ndbapi/en/overview-ndb-api.html" target="_top">
             NDB Cluster API Overview: The NDB API
            </a>
            , for
              more information.
           </p>
          </div>
         </li>
        </ul>
       </div>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-show-nodegroup-star">
       </a>
       <a name="idm46045055978416">
       </a>
       <p>
        <b>
         A.10.7.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        When I run the
        <code class="literal">
         SHOW
        </code>
        command in the NDB
        Cluster management client, I see a line of output that looks
        like this:
       </p>
       <div class="copytoclipboard-wrapper">
        <pre class="programlisting one-line language-none"><div class="docs-select-all right" id="sa77586617"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-none">id=2    @10.100.10.32  (Version: 8.0.41-ndb-8.0.41 Nodegroup: 0, *)</code></pre>
       </div>
       <p>
        What does the
        <code class="literal">
         *
        </code>
        mean? How is this node
        different from the others?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        The simplest answer is,
        <span class="quote">
         “
         <span class="quote">
          It's not something you can
        control, and it's nothing that you need to worry about in
        any case, unless you're a software engineer writing or
        analyzing the NDB Cluster source code
         </span>
         ”
        </span>
        .
       </p>
       <p>
        If you don't find that answer satisfactory, here's a
        longer and more technical version:
       </p>
       <p>
        A number of mechanisms in NDB Cluster require distributed
        coordination among the data nodes. These distributed algorithms
        and protocols include global checkpointing, DDL (schema)
        changes, and node restart handling. To make this coordination
        simpler, the data nodes
        <span class="quote">
         “
         <span class="quote">
          elect
         </span>
         ”
        </span>
        one of their number
        to act as leader. There is no user-facing mechanism for
        influencing this selection, which is completely automatic; the
        fact that it
        <span class="emphasis">
         <em>
          is
         </em>
        </span>
        automatic is a key part of
        NDB Cluster's internal architecture.
       </p>
       <p>
        When a node acts as the
        <span class="quote">
         “
         <span class="quote">
          leader
         </span>
         ”
        </span>
        for any of these
        mechanisms, it is usually the point of coordination for the
        activity, and the other nodes act as
        <span class="quote">
         “
         <span class="quote">
          followers
         </span>
         ”
        </span>
        ,
        carrying out their parts of the activity as directed by the
        leader. If the node acting as leader fails, then the remaining
        nodes elect a new leader. Tasks in progress that were being
        coordinated by the old leader may either fail or be continued by
        the new leader, depending on the actual mechanism involved.
       </p>
       <p>
        It is possible for some of these different mechanisms and
        protocols to have different leader nodes, but in general the
        same leader is chosen for all of them. The node indicated as the
        leader in the output of
        <a class="link" href="mysql-cluster-mgm-client-commands.html#ndbclient-show">
         <code class="literal">
          SHOW
         </code>
        </a>
        in the management client is known internally as the
        <a class="ulink" href="/doc/ndb-internals/en/ndb-internals-kernel-blocks-dbdict.html" target="_top">
         <code class="literal">
          DICT
         </code>
        </a>
        manager, responsible
        for coordinating DDL and metadata activity.
       </p>
       <p>
        NDB Cluster is designed in such a way that the choice of leader
        has no discernible effect outside the cluster itself. For
        example, the current leader does not have significantly higher
        CPU or resource usage than the other data nodes, and failure of
        the leader should not have a significantly different impact on
        the cluster than the failure of any other data node.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-which-os-clustering">
       </a>
       <a name="idm46045055964784">
       </a>
       <p>
        <b>
         A.10.8.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        With which operating systems can I use NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster is supported on most Unix-like operating systems.
        NDB Cluster is also supported in production settings on
        Microsoft Windows operating systems.
       </p>
       <p>
        For more detailed information concerning the level of support
        which is offered for NDB Cluster on various operating system
        versions, operating system distributions, and hardware
        platforms, please refer to
        <a class="ulink" href="https://www.mysql.com/support/supportedplatforms/cluster.html" target="_blank">
         https://www.mysql.com/support/supportedplatforms/cluster.html
        </a>
        .
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-cluster-requirements">
       </a>
       <a name="idm46045055961392">
       </a>
       <p>
        <b>
         A.10.9.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        What are the hardware requirements for running NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster should run on any platform for which
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        -enabled binaries are available.
        For data nodes and API nodes, faster CPUs and more memory are
        likely to improve performance, and 64-bit CPUs are likely to be
        more effective than 32-bit processors. There must be sufficient
        memory on machines used for data nodes to hold each node's share
        of the database (see
        <span class="emphasis">
         <em>
          How much RAM do I
        Need?
         </em>
        </span>
        for more information). For a computer which is
        used only for running the NDB Cluster management server, the
        requirements are minimal; a common desktop PC (or the
        equivalent) is generally sufficient for this task. Nodes can
        communicate through the standard TCP/IP network and hardware.
        They can also use the high-speed SCI protocol; however, special
        networking hardware and software are required to use SCI (see
        <a class="xref" href="mysql-cluster-interconnects.html" title="25.4.4 Using High-Speed Interconnects with NDB Cluster">
         Section 25.4.4, “Using High-Speed Interconnects with NDB Cluster”
        </a>
        ).
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-memory-needed-cluster">
       </a>
       <a name="idm46045055956080">
       </a>
       <p>
        <b>
         A.10.10.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        How much RAM do I need to use NDB Cluster? Is it possible to use
        disk memory at all?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster was originally implemented as in-memory only, but
        all versions currently available also provide the ability to
        store NDB Cluster on disk. See
        <a class="xref" href="mysql-cluster-disk-data.html" title="25.6.11 NDB Cluster Disk Data Tables">
         Section 25.6.11, “NDB Cluster Disk Data Tables”
        </a>
        , for more information.
       </p>
       <p>
        For in-memory
        <code class="literal">
         NDB
        </code>
        tables, you can use the
        following formula for obtaining a rough estimate of how much RAM
        is needed for each data node in the cluster:
       </p>
       <div class="copytoclipboard-wrapper">
        <pre class="programlisting one-line language-simple"><div class="docs-select-all right" id="sa30747490"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-simple"><span class="token punctuation">(</span>SizeofDatabase × NumberOfReplicas × 1<span class="token punctuation">.</span>1 <span class="token punctuation">)</span> <span class="token operator">/</span> NumberOfDataNodes</code></pre>
       </div>
       <p>
        To calculate the memory requirements more exactly requires
        determining, for each table in the cluster database, the storage
        space required per row (see
        <a class="xref" href="storage-requirements.html" title="13.7 Data Type Storage Requirements">
         Section 13.7, “Data Type Storage Requirements”
        </a>
        , for details), and
        multiplying this by the number of rows. You must also remember
        to account for any column indexes as follows:
       </p>
       <div class="itemizedlist">
        <ul class="itemizedlist" style="list-style-type: disc; ">
         <li class="listitem">
          <p>
           Each primary key or hash index created for an
           <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
            <code class="literal">
             NDBCLUSTER
            </code>
           </a>
           table requires
            21−25 bytes per record. These indexes use
           <code class="literal">
            IndexMemory
           </code>
           .
          </p>
         </li>
         <li class="listitem">
          <p>
           Each ordered index requires 10 bytes storage per record,
            using
           <code class="literal">
            DataMemory
           </code>
           .
          </p>
         </li>
         <li class="listitem">
          <p>
           Creating a primary key or unique index also creates an
            ordered index, unless this index is created with
           <code class="literal">
            USING HASH
           </code>
           . In other words:
          </p>
          <div class="itemizedlist">
           <ul class="itemizedlist" style="list-style-type: circle; ">
            <li class="listitem">
             <p>
              A primary key or unique index on a Cluster table
                normally takes up 31 to 35 bytes per record.
             </p>
            </li>
            <li class="listitem">
             <p>
              However, if the primary key or unique index is created
                with
              <code class="literal">
               USING HASH
              </code>
              , then it requires
                only 21 to 25 bytes per record.
             </p>
            </li>
           </ul>
          </div>
         </li>
        </ul>
       </div>
       <p>
        Creating NDB Cluster tables with
        <code class="literal">
         USING HASH
        </code>
        for all primary keys and unique indexes generally causes table
        updates to run more quickly—in some cases by a much as 20
        to 30 percent faster than updates on tables where
        <code class="literal">
         USING
        HASH
        </code>
        was not used in creating primary and unique keys.
        This is due to the fact that less memory is required (because no
        ordered indexes are created), and that less CPU must be utilized
        (because fewer indexes must be read and possibly updated).
        However, it also means that queries that could otherwise use
        range scans must be satisfied by other means, which can result
        in slower selects.
       </p>
       <p>
        When calculating Cluster memory requirements, you may find
        useful the
        <a class="link" href="mysql-cluster-programs-ndb-size-pl.html" title="25.5.29 ndb_size.pl — NDBCLUSTER Size Requirement Estimator">
         <span class="command">
          <strong>
           ndb_size.pl
          </strong>
         </span>
        </a>
        utility which is
        available in recent MySQL 8.4 releases. This Perl
        script connects to a current (non-Cluster) MySQL database and
        creates a report on how much space that database would require
        if it used the
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDBCLUSTER
         </code>
        </a>
        storage
        engine. For more information, see
        <a class="xref" href="mysql-cluster-programs-ndb-size-pl.html" title="25.5.29 ndb_size.pl — NDBCLUSTER Size Requirement Estimator">
         Section 25.5.29, “ndb_size.pl — NDBCLUSTER Size Requirement Estimator”
        </a>
        .
       </p>
       <p>
        It is especially important to keep in mind that
        <span class="emphasis">
         <em>
          every
        NDB Cluster table must have a primary key
         </em>
        </span>
        . The
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        storage engine creates a
        primary key automatically if none is defined; this primary key
        is created without
        <code class="literal">
         USING HASH
        </code>
        .
       </p>
       <p>
        You can determine how much memory is being used for storage of
        NDB Cluster data and indexes at any given time using the
        <code class="literal">
         REPORT MEMORYUSAGE
        </code>
        command in the
        <a class="link" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
         <span class="command">
          <strong>
           ndb_mgm
          </strong>
         </span>
        </a>
        client; see
        <a class="xref" href="mysql-cluster-mgm-client-commands.html" title="25.6.1 Commands in the NDB Cluster Management Client">
         Section 25.6.1, “Commands in the NDB Cluster Management Client”
        </a>
        , for more
        information. In addition, warnings are written to the cluster
        log when 80% of available
        <a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-datamemory">
         <code class="literal">
          DataMemory
         </code>
        </a>
        or (prior to
        NDB 7.6)
        <a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-indexmemory">
         <code class="literal">
          IndexMemory
         </code>
        </a>
        is
        in use, and again when usage reaches 90%, 99%, and 100%.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-cluster-file-systems">
       </a>
       <a name="idm46045055924320">
       </a>
       <p>
        <b>
         A.10.11.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        What file systems can I use with NDB Cluster? What about network
        file systems or network shares?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        Generally, any file system that is native to the host operating
        system should work well with NDB Cluster. If you find that a
        given file system works particularly well (or not so especially
        well) with NDB Cluster, we invite you to discuss your findings
        in the
        <a class="ulink" href="https://forums.mysql.com/list.php?25" target="_blank">
         NDB Cluster
        Forums
        </a>
        .
       </p>
       <p>
        For Windows, we recommend that you use
        <code class="literal">
         NTFS
        </code>
        file systems for NDB Cluster, just as we do for standard MySQL.
        We do not test NDB Cluster with
        <code class="literal">
         FAT
        </code>
        or
        <code class="literal">
         VFAT
        </code>
        file systems. Because of this, we do not
        recommend their use with MySQL or NDB Cluster.
       </p>
       <p>
        NDB Cluster is implemented as a shared-nothing solution; the
        idea behind this is that the failure of a single piece of
        hardware should not cause the failure of multiple cluster nodes,
        or possibly even the failure of the cluster as a whole. For this
        reason, the use of network shares or network file systems is not
        supported for NDB Cluster. This also applies to shared storage
        devices such as SANs.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-can-cluster-vm">
       </a>
       <a name="idm46045055917584">
       </a>
       <p>
        <b>
         A.10.12.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Can I run NDB Cluster nodes inside virtual machines (such as
        those created by VMWare, VirtualBox, Parallels, or Xen)?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster is supported for use in virtual machines. We
        currently support and test using
        <a class="ulink" href="http://www.oracle.com/technetwork/server-storage/vm/index.html" target="_blank">
         Oracle
        VM
        </a>
        .
       </p>
       <p>
        Some NDB Cluster users have successfully deployed NDB Cluster
        using other virtualization products; in such cases, Oracle can
        provide NDB Cluster support, but issues specific to the virtual
        environment must be referred to that product's vendor.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-why-error-1114">
       </a>
       <a name="idm46045055913984">
       </a>
       <p>
        <b>
         A.10.13.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        I am trying to populate an NDB Cluster database. The loading
        process terminates prematurely and I get an error message like
        this one:
       </p>
       <p>
        <code class="literal">
         <span class="errortext">
          ERROR 1114: The table 'my_cluster_table' is
        full
         </span>
        </code>
       </p>
       <p>
        Why is this happening?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        The cause is very likely to be that your setup does not provide
        sufficient RAM for all table data and all indexes,
        <span class="emphasis">
         <em>
          including the primary key required by the
          <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
           <code class="literal">
            NDB
           </code>
          </a>
          storage engine and
        automatically created in the event that the table definition
        does not include the definition of a primary key
         </em>
        </span>
        .
       </p>
       <p>
        It is also worth noting that all data nodes should have the same
        amount of RAM, since no data node in a cluster can use more
        memory than the least amount available to any individual data
        node. For example, if there are four computers hosting Cluster
        data nodes, and three of these have 3GB of RAM available to
        store Cluster data while the remaining data node has only 1GB
        RAM, then each data node can devote at most 1GB to NDB Cluster
        data and indexes.
       </p>
       <p>
        In some cases it is possible to get
        <span class="errortext">
         Table is
        full
        </span>
        errors in MySQL client applications even when
        <a class="link" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
         <span class="command">
          <strong>
           ndb_mgm -e "ALL REPORT MEMORYUSAGE"
          </strong>
         </span>
        </a>
        shows
        significant free
        <a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-datamemory">
         <code class="literal">
          DataMemory
         </code>
        </a>
        . You can
        force
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        to create extra
        partitions for NDB Cluster tables and thus have more memory
        available for hash indexes by using the
        <code class="literal">
         MAX_ROWS
        </code>
        option for
        <a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
         <code class="literal">
          CREATE TABLE
         </code>
        </a>
        . In general, setting
        <code class="literal">
         MAX_ROWS
        </code>
        to twice the number of rows that you
        expect to store in the table should be sufficient.
       </p>
       <p>
        For similar reasons, you can also sometimes encounter problems
        with data node restarts on nodes that are heavily loaded with
        data. The
        <a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-minfreepct" title="MinFreePct">
         <code class="literal">
          MinFreePct
         </code>
        </a>
        parameter can help with this issue by reserving a portion (5% by
        default) of
        <a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-datamemory">
         <code class="literal">
          DataMemory
         </code>
        </a>
        and (prior to NDB 7.6)
        <a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-indexmemory">
         <code class="literal">
          IndexMemory
         </code>
        </a>
        for use in
        restarts. This reserved memory is not available for storing
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        tables or data.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-can-cluster-remote-network">
       </a>
       <a name="idm46045055893952">
       </a>
       <p>
        <b>
         A.10.14.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster uses TCP/IP. Does this mean that I can run it over
        the Internet, with one or more nodes in remote locations?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        It is
        <span class="emphasis">
         <em>
          very
         </em>
        </span>
        unlikely that a cluster would
        perform reliably under such conditions, as NDB Cluster was
        designed and implemented with the assumption that it would be
        run under conditions guaranteeing dedicated high-speed
        connectivity such as that found in a LAN setting using 100 Mbps
        or gigabit Ethernet—preferably the latter. We neither test
        nor warrant its performance using anything slower than this.
       </p>
       <p>
        Also, it is extremely important to keep in mind that
        communications between the nodes in an NDB Cluster are not
        secure; they are neither encrypted nor safeguarded by any other
        protective mechanism. The most secure configuration for a
        cluster is in a private network behind a firewall, with no
        direct access to any Cluster data or management nodes from
        outside. (For SQL nodes, you should take the same precautions as
        you would with any other instance of the MySQL server.) For more
        information, see
        <a class="xref" href="mysql-cluster-security.html" title="25.6.21 NDB Cluster Security Issues">
         Section 25.6.21, “NDB Cluster Security Issues”
        </a>
        .
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-language-needed-cluster">
       </a>
       <a name="idm46045055888880">
       </a>
       <p>
        <b>
         A.10.15.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Do I have to learn a new programming or query language to use
        NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        <span class="emphasis">
         <em>
          No
         </em>
        </span>
        . Although some specialized commands are
        used to manage and configure the cluster itself, only standard
        (My)SQL statements are required for the following operations:
       </p>
       <div class="itemizedlist">
        <ul class="itemizedlist" style="list-style-type: disc; ">
         <li class="listitem">
          <p>
           Creating, altering, and dropping tables
          </p>
         </li>
         <li class="listitem">
          <p>
           Inserting, updating, and deleting table data
          </p>
         </li>
         <li class="listitem">
          <p>
           Creating, changing, and dropping primary and unique indexes
          </p>
         </li>
        </ul>
       </div>
       <p>
        Some specialized configuration parameters and files are required
        to set up an NDB Cluster—see
        <a class="xref" href="mysql-cluster-config-file.html" title="25.4.3 NDB Cluster Configuration Files">
         Section 25.4.3, “NDB Cluster Configuration Files”
        </a>
        , for information
        about these.
       </p>
       <p>
        A few simple commands are used in the NDB Cluster management
        client (
        <a class="link" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
         <span class="command">
          <strong>
           ndb_mgm
          </strong>
         </span>
        </a>
        ) for tasks such as starting
        and stopping cluster nodes. See
        <a class="xref" href="mysql-cluster-mgm-client-commands.html" title="25.6.1 Commands in the NDB Cluster Management Client">
         Section 25.6.1, “Commands in the NDB Cluster Management Client”
        </a>
        .
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-api-cluster-support">
       </a>
       <a name="idm46045055879440">
       </a>
       <p>
        <b>
         A.10.16.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        What programming languages and APIs are supported by NDB
        Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster supports the same programming APIs and languages as
        the standard MySQL Server, including ODBC, .Net, the MySQL C
        API, and numerous drivers for popular scripting languages such
        as PHP, Perl, and Python. NDB Cluster applications written using
        these APIs behave similarly to other MySQL applications; they
        transmit SQL statements to a MySQL Server (in the case of NDB
        Cluster, an SQL node), and receive responses containing rows of
        data. For more information about these APIs, see
        <a class="xref" href="connectors-apis.html" title="Chapter 31 Connectors and APIs">
         Chapter 31,
         <i>
          Connectors and APIs
         </i>
        </a>
        .
       </p>
       <p>
        NDB Cluster also supports application programming using the NDB
        API, which provides a low-level C++ interface to NDB Cluster
        data without needing to go through a MySQL Server. See
        <a class="ulink" href="/doc/ndbapi/en/ndbapi.html" target="_top">
         The NDB API
        </a>
        . In addition, many
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDBCLUSTER
         </code>
        </a>
        management functions are
        exposed by the C-language MGM API; see
        <a class="ulink" href="/doc/ndbapi/en/mgm-api.html" target="_top">
         The MGM API
        </a>
        , for more information.
       </p>
       <p>
        NDB Cluster also supports Java application programming using
        ClusterJ, which supports a domain object model of data using
        sessions and transactions. See
        <a class="ulink" href="/doc/ndbapi/en/mccj-overview-java.html" target="_top">
         Java and NDB Cluster
        </a>
        , for more information.
       </p>
       <p>
        NDB Cluster 8.0 also includes adapters supporting NoSQL
        applications written against
        <code class="literal">
         Node.js
        </code>
        , with
        NDB Cluster as the data store. See
        <a class="ulink" href="/doc/ndbapi/en/ndb-nodejs.html" target="_top">
         MySQL NoSQL Connector for JavaScript
        </a>
        ,
        for more information.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-cluster-management-tools">
       </a>
       <a name="idm46045055869328">
       </a>
       <p>
        <b>
         A.10.17.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Does NDB Cluster include any management tools?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster includes a command line client for performing basic
        management functions. See
        <a class="xref" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
         Section 25.5.5, “ndb_mgm — The NDB Cluster Management Client”
        </a>
        , and
        <a class="xref" href="mysql-cluster-mgm-client-commands.html" title="25.6.1 Commands in the NDB Cluster Management Client">
         Section 25.6.1, “Commands in the NDB Cluster Management Client”
        </a>
        .
       </p>
       <p>
        NDB Cluster is also supported by MySQL Cluster Manager, a separate product
        providing an advanced command line interface that can automate
        many NDB Cluster management tasks such as rolling restarts and
        configuration changes. For more information about MySQL Cluster Manager, see
        <a class="ulink" href="/doc/mysql-cluster-manager/8.4/en/" target="_top">
         MySQL Cluster Manager 8.4.3 User Manual
        </a>
        .
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-cluster-errors-are">
       </a>
       <a name="idm46045055864320">
       </a>
       <p>
        <b>
         A.10.18.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        How do I find out what an error or warning message means when
        using NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        There are two ways in which this can be done:
       </p>
       <div class="itemizedlist">
        <ul class="itemizedlist" style="list-style-type: disc; ">
         <li class="listitem">
          <p>
           From within the
           <a class="link" href="mysql.html" title="6.5.1 mysql — The MySQL Command-Line Client">
            <span class="command">
             <strong>
              mysql
             </strong>
            </span>
           </a>
           client, use
           <span class="command">
            <strong>
             SHOW ERRORS
            </strong>
           </span>
           or
           <span class="command">
            <strong>
             SHOW
            WARNINGS
            </strong>
           </span>
           immediately upon being notified of the
            error or warning condition.
          </p>
         </li>
         <li class="listitem">
          <p>
           From a system shell prompt, use
           <a class="link" href="perror.html" title="6.8.1 perror — Display MySQL Error Message Information">
            <span class="command">
             <strong>
              perror --ndb
              <em class="replaceable">
               <code>
                error_code
               </code>
              </em>
             </strong>
            </span>
           </a>
           .
          </p>
         </li>
        </ul>
       </div>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-is-cluster-transaction-safe">
       </a>
       <a name="idm46045055855840">
       </a>
       <p>
        <b>
         A.10.19.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Is NDB Cluster transaction-safe? What isolation levels are
        supported?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        <span class="emphasis">
         <em>
          Yes
         </em>
        </span>
        . For tables created with the
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        storage engine, transactions
        are supported. Currently, NDB Cluster supports only the
        <a class="link" href="innodb-transaction-isolation-levels.html#isolevel_read-committed">
         <code class="literal">
          READ COMMITTED
         </code>
        </a>
        transaction
        isolation level.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-storage-engines-cluster">
       </a>
       <a name="idm46045055850784">
       </a>
       <p>
        <b>
         A.10.20.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        What storage engines are supported by NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster requires the
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        storage engine. That is, in order for a table to be shared
        between nodes in an NDB Cluster, the table must be created using
        <code class="literal">
         ENGINE=NDB
        </code>
        (or the equivalent option
        <code class="literal">
         ENGINE=NDBCLUSTER
        </code>
        ).
       </p>
       <p>
        It is possible to create tables using other storage engines
        (such as
        <a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
         <code class="literal">
          InnoDB
         </code>
        </a>
        or
        <a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
         <code class="literal">
          MyISAM
         </code>
        </a>
        ) on a MySQL server being
        used with NDB Cluster, but since these tables do not use
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        , they do not participate in
        clustering; each such table is strictly local to the individual
        MySQL server instance on which it is created.
       </p>
       <p>
        NDB Cluster is quite different from
        <a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
         <code class="literal">
          InnoDB
         </code>
        </a>
        clustering with regard to
        architecture, requirements, and implementation; despite any
        similarity in their names, the two are not compatible. For more
        information about
        <code class="literal">
         InnoDB
        </code>
        clustering, see
        <a class="ulink" href="/doc/mysql-shell/8.4/en/admin-api-userguide.html" target="_top">
         MySQL AdminAPI
        </a>
        . See also
        <a class="xref" href="mysql-cluster-compared.html" title="25.2.6 MySQL Server Using InnoDB Compared with NDB Cluster">
         Section 25.2.6, “MySQL Server Using InnoDB Compared with NDB Cluster”
        </a>
        , for information about
        the differences between the
        <code class="literal">
         NDB
        </code>
        and
        <code class="literal">
         InnoDB
        </code>
        storage engines.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-is-data-loss-no-power">
       </a>
       <a name="idm46045055836096">
       </a>
       <p>
        <b>
         A.10.21.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        In the event of a catastrophic failure— for example, the
        whole city loses power
        <span class="emphasis">
         <em>
          and
         </em>
        </span>
        my UPS
        fails—would I lose all my data?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        All committed transactions are logged. Therefore, although it is
        possible that some data could be lost in the event of a
        catastrophe, this should be quite limited. Data loss can be
        further reduced by minimizing the number of operations per
        transaction. (It is not a good idea to perform large numbers of
        operations per transaction in any case.)
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-can-cluster-fullindex">
       </a>
       <a name="idm46045055833040">
       </a>
       <p>
        <b>
         A.10.22.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Is it possible to use
        <code class="literal">
         FULLTEXT
        </code>
        indexes with
        NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        <code class="literal">
         FULLTEXT
        </code>
        indexing is currently supported only
        by the
        <a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
         <code class="literal">
          InnoDB
         </code>
        </a>
        and
        <a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
         <code class="literal">
          MyISAM
         </code>
        </a>
        storage engines. See
        <a class="xref" href="fulltext-search.html" title="14.9 Full-Text Search Functions">
         Section 14.9, “Full-Text Search Functions”
        </a>
        , for more information.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-can-multinode-cluster-one-host">
       </a>
       <a name="idm46045055826320">
       </a>
       <p>
        <b>
         A.10.23.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Can I run multiple nodes on a single computer?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        It is possible but not always advisable. One of the chief
        reasons to run a cluster is to provide redundancy. To obtain the
        full benefits of this redundancy, each node should reside on a
        separate machine. If you place multiple nodes on a single
        machine and that machine fails, you lose all of those nodes. For
        this reason, if you do run multiple data nodes on a single
        machine, it is
        <span class="emphasis">
         <em>
          extremely
         </em>
        </span>
        important that
        they be set up in such a way that the failure of this machine
        does not cause the loss of all the data nodes in a given node
        group.
       </p>
       <p>
        Given that NDB Cluster can be run on commodity hardware loaded
        with a low-cost (or even no-cost) operating system, the expense
        of an extra machine or two is well worth it to safeguard
        mission-critical data. It also worth noting that the
        requirements for a cluster host running a management node are
        minimal. This task can be accomplished with a 300 MHz Pentium or
        equivalent CPU and sufficient RAM for the operating system, plus
        a small amount of overhead for the
        <a class="link" href="mysql-cluster-programs-ndb-mgmd.html" title="25.5.4 ndb_mgmd — The NDB Cluster Management Server Daemon">
         <span class="command">
          <strong>
           ndb_mgmd
          </strong>
         </span>
        </a>
        and
        <a class="link" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
         <span class="command">
          <strong>
           ndb_mgm
          </strong>
         </span>
        </a>
        processes.
       </p>
       <p>
        It is acceptable to run multiple cluster data nodes on a single
        host that has multiple CPUs, cores, or both. The NDB Cluster
        distribution also provides a multithreaded version of the data
        node binary intended for use on such systems. For more
        information, see
        <a class="xref" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
         Section 25.5.3, “ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)”
        </a>
        .
       </p>
       <p>
        It is also possible in some cases to run data nodes and SQL
        nodes concurrently on the same machine; how well such an
        arrangement performs is dependent on a number of factors such as
        number of cores and CPUs as well as the amount of disk and
        memory available to the data node and SQL node processes, and
        you must take these factors into account when planning such a
        configuration.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-how-add-nodes-no-restart">
       </a>
       <a name="idm46045055817584">
       </a>
       <p>
        <b>
         A.10.24.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Can I add data nodes to an NDB Cluster without restarting it?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        It is possible to add new data nodes to a running NDB Cluster
        without taking the cluster offline. For more information, see
        <a class="xref" href="mysql-cluster-online-add-node.html" title="25.6.7 Adding NDB Cluster Data Nodes Online">
         Section 25.6.7, “Adding NDB Cluster Data Nodes Online”
        </a>
        .
       </p>
       <p>
        For other types of NDB Cluster nodes, a rolling restart is all
        that is required (see
        <a class="xref" href="mysql-cluster-rolling-restart.html" title="25.6.5 Performing a Rolling Restart of an NDB Cluster">
         Section 25.6.5, “Performing a Rolling Restart of an NDB Cluster”
        </a>
        ).
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-cluster-limitations">
       </a>
       <a name="idm46045055813488">
       </a>
       <p>
        <b>
         A.10.25.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Are there any limitations that I should be aware of when using
        NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        Limitations on
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        tables in MySQL
        NDB Cluster include the following:
       </p>
       <div class="itemizedlist">
        <ul class="itemizedlist" style="list-style-type: disc; ">
         <li class="listitem">
          <p>
           Temporary tables are not supported; a
           <a class="link" href="create-table.html" title="15.1.20 CREATE TABLE Statement">
            <code class="literal">
             CREATE
            TEMPORARY TABLE
            </code>
           </a>
           statement using
           <code class="literal">
            ENGINE=NDB
           </code>
           or
           <code class="literal">
            ENGINE=NDBCLUSTER
           </code>
           fails with an error.
          </p>
         </li>
         <li class="listitem">
          <p>
           The only types of user-defined partitioning supported for
           <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
            <code class="literal">
             NDBCLUSTER
            </code>
           </a>
           tables are
           <code class="literal">
            KEY
           </code>
           and
           <code class="literal">
            LINEAR KEY
           </code>
           .
            Trying to create an
           <code class="literal">
            NDB
           </code>
           table using any
            other partitioning type fails with an error.
          </p>
         </li>
         <li class="listitem">
          <p>
           <code class="literal">
            FULLTEXT
           </code>
           indexes are not supported.
          </p>
         </li>
         <li class="listitem">
          <p>
           Index prefixes are not supported. Only complete columns may
            be indexed.
          </p>
         </li>
         <li class="listitem">
          <p>
           Spatial indexes are not supported (although spatial columns
            can be used). See
           <a class="xref" href="spatial-types.html" title="13.4 Spatial Data Types">
            Section 13.4, “Spatial Data Types”
           </a>
           .
          </p>
         </li>
         <li class="listitem">
          <p>
           Support for partial transactions and partial rollbacks is
            comparable to that of other transactional storage engines
            such as
           <a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
            <code class="literal">
             InnoDB
            </code>
           </a>
           that can roll
            back individual statements.
          </p>
         </li>
         <li class="listitem">
          <p>
           The maximum number of attributes allowed per table is 512.
            Attribute names cannot be any longer than 31 characters. For
            each table, the maximum combined length of the table and
            database names is 122 characters.
          </p>
         </li>
         <li class="listitem">
          <p>
           Priot to NDB 8.0, the maximum size for a table row is 14
            kilobytes, not counting
           <a class="link" href="blob.html" title="13.3.4 The BLOB and TEXT Types">
            <code class="literal">
             BLOB
            </code>
           </a>
           values. In NDB 8.0, this maximum is increased to 30000
            bytes. See
           <a class="xref" href="mysql-cluster-limitations-database-objects.html" title="25.2.7.5 Limits Associated with Database Objects in NDB Cluster">
            Section 25.2.7.5, “Limits Associated with Database Objects in NDB Cluster”
           </a>
           ,
            for more information.
          </p>
          <p>
           There is no set limit for the number of rows per
           <code class="literal">
            NDB
           </code>
           table. Limits on table size depend on
            a number of factors, in particular on the amount of RAM
            available to each data node.
          </p>
         </li>
        </ul>
       </div>
       <p>
        For a complete listing of limitations in NDB Cluster, see
        <a class="xref" href="mysql-cluster-limitations.html" title="25.2.7 Known Limitations of NDB Cluster">
         Section 25.2.7, “Known Limitations of NDB Cluster”
        </a>
        . See also
        <a class="xref" href="mysql-cluster-limitations-resolved.html" title="25.2.7.11 Previous NDB Cluster Issues Resolved in NDB Cluster 8.4">
         Section 25.2.7.11, “Previous NDB Cluster Issues Resolved in NDB Cluster 8.4”
        </a>
        .
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-have-foreign-keys-cluster">
       </a>
       <a name="idm46045055788576">
       </a>
       <p>
        <b>
         A.10.26.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Does NDB Cluster support foreign keys?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster provides support for foreign key constraints which
        is comparable to that found in the
        <a class="link" href="innodb-storage-engine.html" title="Chapter 17 The InnoDB Storage Engine">
         <code class="literal">
          InnoDB
         </code>
        </a>
        storage engine; see
        <a class="xref" href="constraint-foreign-key.html" title="1.7.3.2 FOREIGN KEY Constraints">
         Section 1.7.3.2, “FOREIGN KEY Constraints”
        </a>
        , for more detailed
        information, as well as
        <a class="xref" href="create-table-foreign-keys.html" title="15.1.20.5 FOREIGN KEY Constraints">
         Section 15.1.20.5, “FOREIGN KEY Constraints”
        </a>
        . Applications
        requiring foreign key support should use NDB Cluster 7.3, 7.4,
        7.5, or later.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-how-import-db-cluster">
       </a>
       <a name="idm46045055783744">
       </a>
       <p>
        <b>
         A.10.27.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        How do I import an existing MySQL database into an NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        You can import databases into NDB Cluster much as you would with
        any other version of MySQL. Other than the limitations mentioned
        elsewhere in this FAQ, the only other special requirement is
        that any tables to be included in the cluster must use the
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        storage engine. This means that
        the tables must be created with
        <code class="literal">
         ENGINE=NDB
        </code>
        or
        <code class="literal">
         ENGINE=NDBCLUSTER
        </code>
        .
       </p>
       <p>
        It is also possible to convert existing tables that use other
        storage engines to
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDBCLUSTER
         </code>
        </a>
        using
        one or more
        <a class="link" href="alter-table.html" title="15.1.9 ALTER TABLE Statement">
         <code class="literal">
          ALTER TABLE
         </code>
        </a>
        statement. However, the definition of the table must be
        compatible with the
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDBCLUSTER
         </code>
        </a>
        storage engine prior to making the conversion. In MySQL
        8.4, an additional workaround is also required; see
        <a class="xref" href="mysql-cluster-limitations.html" title="25.2.7 Known Limitations of NDB Cluster">
         Section 25.2.7, “Known Limitations of NDB Cluster”
        </a>
        , for details.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-how-nodes-communicate">
       </a>
       <a name="idm46045055773680">
       </a>
       <p>
        <b>
         A.10.28.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        How do NDB Cluster nodes communicate with one another?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        Cluster nodes can communicate through any of three different
        transport mechanisms: TCP/IP, SHM (shared memory), and SCI
        (Scalable Coherent Interface). Where available, SHM is used by
        default between nodes residing on the same cluster host;
        however, this is considered experimental. SCI is a high-speed (1
        gigabit per second and higher), high-availability protocol used
        in building scalable multi-processor systems; it requires
        special hardware and drivers. See
        <a class="xref" href="mysql-cluster-interconnects.html" title="25.4.4 Using High-Speed Interconnects with NDB Cluster">
         Section 25.4.4, “Using High-Speed Interconnects with NDB Cluster”
        </a>
        , for more about
        using SCI as a transport mechanism for NDB Cluster.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-is-arbitrator">
       </a>
       <a name="idm46045055770432">
       </a>
       <p>
        <b>
         A.10.29.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        What is an
        <span class="firstterm">
         arbitrator
        </span>
        ?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        If one or more data nodes in a cluster fail, it is possible that
        not all cluster data nodes are able to
        <span class="quote">
         “
         <span class="quote">
          see
         </span>
         ”
        </span>
        one
        another. In fact, it is possible that two sets of data nodes
        might become isolated from one another in a network
        partitioning, also known as a
        <span class="quote">
         “
         <span class="quote">
          split-brain
         </span>
         ”
        </span>
        scenario. This type of situation is undesirable because each set
        of data nodes tries to behave as though it is the entire
        cluster. An arbitrator is required to decide between the
        competing sets of data nodes.
       </p>
       <p>
        When all data nodes in at least one node group are alive,
        network partitioning is not an issue, because no single subset
        of the cluster can form a functional cluster on its own. The
        real problem arises when no single node group has all its nodes
        alive, in which case network partitioning (the
        <span class="quote">
         “
         <span class="quote">
          split-brain
         </span>
         ”
        </span>
        scenario) becomes possible. Then an
        arbitrator is required. All cluster nodes recognize the same
        node as the arbitrator, which is normally the management server;
        however, it is possible to configure any of the MySQL Servers in
        the cluster to act as the arbitrator instead. The arbitrator
        accepts the first set of cluster nodes to contact it, and tells
        the remaining set to shut down. Arbitrator selection is
        controlled by the
        <code class="literal">
         ArbitrationRank
        </code>
        configuration parameter for MySQL Server and management server
        nodes. You can also use the
        <code class="literal">
         ArbitrationRank
        </code>
        configuration parameter to control the arbitrator selection
        process. For more information about these parameters, see
        <a class="xref" href="mysql-cluster-mgm-definition.html" title="25.4.3.5 Defining an NDB Cluster Management Server">
         Section 25.4.3.5, “Defining an NDB Cluster Management Server”
        </a>
        .
       </p>
       <p>
        The role of arbitrator does not in and of itself impose any
        heavy demands upon the host so designated, and thus the
        arbitrator host does not need to be particularly fast or to have
        extra memory especially for this purpose.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-types-cluster-support">
       </a>
       <a name="idm46045055761744">
       </a>
       <p>
        <b>
         A.10.30.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        What data types are supported by NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        NDB Cluster supports all of the usual MySQL data types,
        including those associated with MySQL's spatial extensions;
        however, the
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        storage engine
        does not support spatial indexes. (Spatial indexes are supported
        only by
        <a class="link" href="myisam-storage-engine.html" title="18.2 The MyISAM Storage Engine">
         <code class="literal">
          MyISAM
         </code>
        </a>
        ; see
        <a class="xref" href="spatial-types.html" title="13.4 Spatial Data Types">
         Section 13.4, “Spatial Data Types”
        </a>
        , for more information.) In
        addition, there are some differences with regard to indexes when
        used with
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        tables.
       </p>
       <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
        <div class="admon-title">
         Note
        </div>
        <p>
         NDB Cluster Disk Data tables (that is, tables created with
         <code class="literal">
          TABLESPACE ... STORAGE DISK ENGINE=NDB
         </code>
         or
         <code class="literal">
          TABLESPACE ... STORAGE DISK
          ENGINE=NDBCLUSTER
         </code>
         ) have only fixed-width rows. This
          means that (for example) each Disk Data table record
          containing a
         <a class="link" href="char.html" title="13.3.2 The CHAR and VARCHAR Types">
          <code class="literal">
           VARCHAR(255)
          </code>
         </a>
         column requires space for 255 characters (as required for the
          character set and collation being used for the table),
          regardless of the actual number of characters stored therein.
        </p>
       </div>
       <p>
        See
        <a class="xref" href="mysql-cluster-limitations.html" title="25.2.7 Known Limitations of NDB Cluster">
         Section 25.2.7, “Known Limitations of NDB Cluster”
        </a>
        , for more
        information about these issues.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-how-start-stop-cluster">
       </a>
       <a name="idm46045055750000">
       </a>
       <p>
        <b>
         A.10.31.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        How do I start and stop NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        It is necessary to start each node in the cluster separately, in
        the following order:
       </p>
       <div class="orderedlist">
        <ol class="orderedlist" type="1">
         <li class="listitem">
          <p>
           Start the management node, using the
           <a class="link" href="mysql-cluster-programs-ndb-mgmd.html" title="25.5.4 ndb_mgmd — The NDB Cluster Management Server Daemon">
            <span class="command">
             <strong>
              ndb_mgmd
             </strong>
            </span>
           </a>
           command.
          </p>
          <p>
           When starting the cluster for the first time, you must
            include the
           <a class="link" href="mysql-cluster-programs-ndb-mgmd.html#option_ndb_mgmd_config-file">
            <code class="option">
             -f
            </code>
           </a>
           or
           <a class="link" href="mysql-cluster-programs-ndb-mgmd.html#option_ndb_mgmd_config-file">
            <code class="option">
             --config-file
            </code>
           </a>
           option to
            tell the management node where its configuration file can be
            found.
          </p>
         </li>
         <li class="listitem">
          <p>
           Start each data node with the
           <a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
            <span class="command">
             <strong>
              ndbd
             </strong>
            </span>
           </a>
           command.
          </p>
          <p>
           Each data node must be started with the
           <a class="link" href="mysql-cluster-programs-ndbd.html#option_ndbd_ndb-connectstring">
            <code class="option">
             -c
            </code>
           </a>
           or
           <a class="link" href="mysql-cluster-programs-ndbd.html#option_ndbd_ndb-connectstring">
            <code class="option">
             --ndb-connectstring
            </code>
           </a>
           option
            so that the data node knows how to connect to the management
            server.
          </p>
         </li>
         <li class="listitem">
          <p>
           Start each MySQL Server (SQL node) using your preferred
            startup script, such as
           <a class="link" href="mysqld-safe.html" title="6.3.2 mysqld_safe — MySQL Server Startup Script">
            <span class="command">
             <strong>
              mysqld_safe
             </strong>
            </span>
           </a>
           .
          </p>
          <p>
           Each MySQL Server must be started with the
           <a class="link" href="mysql-cluster-options-variables.html#option_mysqld_ndbcluster">
            <code class="option">
             --ndbcluster
            </code>
           </a>
           and
           <a class="link" href="mysql-cluster-options-variables.html#option_mysqld_ndb-connectstring">
            <code class="option">
             --ndb-connectstring
            </code>
           </a>
           options.
            These options cause
           <a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
            <span class="command">
             <strong>
              mysqld
             </strong>
            </span>
           </a>
           to enable
           <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
            <code class="literal">
             NDBCLUSTER
            </code>
           </a>
           storage engine
            support and how to connect to the management server.
          </p>
         </li>
        </ol>
       </div>
       <p>
        Each of these commands must be run from a system shell on the
        machine housing the affected node. (You do not have to be
        physically present at the machine—a remote login shell can
        be used for this purpose.) You can verify that the cluster is
        running by starting the
        <a class="link" href="mysql-cluster.html" title="Chapter 25 MySQL NDB Cluster 8.4">
         <code class="literal">
          NDB
         </code>
        </a>
        management client
        <a class="link" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
         <span class="command">
          <strong>
           ndb_mgm
          </strong>
         </span>
        </a>
        on the machine
        housing the management node and issuing the
        <code class="literal">
         SHOW
        </code>
        or
        <code class="literal">
         ALL STATUS
        </code>
        command.
       </p>
       <p>
        To shut down a running cluster, issue the command
        <code class="literal">
         SHUTDOWN
        </code>
        in the management client.
        Alternatively, you may enter the following command in a system
        shell:
       </p>
       <div class="copytoclipboard-wrapper">
        <pre class="programlisting one-line language-terminal"><div class="docs-select-all right" id="sa71880820"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$&gt; </span><span class="token command">ndb_mgm</span> <span class="token property">-e</span> <span class="token atrule">"SHUTDOWN"</span></code></pre>
       </div>
       <p>
        (The quotation marks in this example are optional, since there
        are no spaces in the command string following the
        <code class="option">
         -e
        </code>
        option; in addition, the
        <code class="literal">
         SHUTDOWN
        </code>
        command, like other management
        client commands, is not case-sensitive.)
       </p>
       <p>
        Either of these commands causes the
        <a class="link" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
         <span class="command">
          <strong>
           ndb_mgm
          </strong>
         </span>
        </a>
        ,
        <a class="link" href="mysql-cluster-programs-ndb-mgm.html" title="25.5.5 ndb_mgm — The NDB Cluster Management Client">
         <span class="command">
          <strong>
           ndb_mgm
          </strong>
         </span>
        </a>
        , and any
        <a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
         <span class="command">
          <strong>
           ndbd
          </strong>
         </span>
        </a>
        processes to terminate gracefully. MySQL servers running as SQL
        nodes can be stopped using
        <a class="link" href="mysqladmin.html" title="6.5.2 mysqladmin — A MySQL Server Administration Program">
         <span class="command">
          <strong>
           mysqladmin
        shutdown
          </strong>
         </span>
        </a>
        .
       </p>
       <p>
        For more information, see
        <a class="xref" href="mysql-cluster-mgm-client-commands.html" title="25.6.1 Commands in the NDB Cluster Management Client">
         Section 25.6.1, “Commands in the NDB Cluster Management Client”
        </a>
        , and
        <a class="xref" href="mysql-cluster-install-shutdown-restart.html" title="25.3.6 Safe Shutdown and Restart of NDB Cluster">
         Section 25.3.6, “Safe Shutdown and Restart of NDB Cluster”
        </a>
        .
       </p>
       <p>
        MySQL Cluster Manager provides additional ways to handle starting ansd stopping
        of NDB Cluster nodes. See
        <a class="ulink" href="/doc/mysql-cluster-manager/8.4/en/" target="_top">
         MySQL Cluster Manager 8.4.3 User Manual
        </a>
        , for more
        information about this tool.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-shutdown-do-data">
       </a>
       <a name="idm46045055712032">
       </a>
       <p>
        <b>
         A.10.32.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        What happens to NDB Cluster data when the cluster is shut down?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        The data that was held in memory by the cluster's data
        nodes is written to disk, and is reloaded into memory the next
        time that the cluster is started.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-have-multiple-node-managers">
       </a>
       <a name="idm46045055709824">
       </a>
       <p>
        <b>
         A.10.33.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Is it a good idea to have more than one management node for an
        NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        It can be helpful as a fail-safe. Only one management node
        controls the cluster at any given time, but it is possible to
        configure one management node as primary, and one or more
        additional management nodes to take over in the event that the
        primary management node fails.
       </p>
       <p>
        See
        <a class="xref" href="mysql-cluster-config-file.html" title="25.4.3 NDB Cluster Configuration Files">
         Section 25.4.3, “NDB Cluster Configuration Files”
        </a>
        , for information
        on how to configure NDB Cluster management nodes.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-have-different-cluster-hosts">
       </a>
       <a name="idm46045055706288">
       </a>
       <p>
        <b>
         A.10.34.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Can I mix different kinds of hardware and operating systems in
        one NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        Yes, as long as all machines and operating systems have the same
        <span class="quote">
         “
         <span class="quote">
          endianness
         </span>
         ”
        </span>
        (all big-endian or all little-endian).
       </p>
       <p>
        It is also possible to use software from different NDB Cluster
        releases on different nodes. However, we support such use only
        as part of a rolling upgrade procedure (see
        <a class="xref" href="mysql-cluster-rolling-restart.html" title="25.6.5 Performing a Rolling Restart of an NDB Cluster">
         Section 25.6.5, “Performing a Rolling Restart of an NDB Cluster”
        </a>
        ).
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-have-multiple-nodes-one-host">
       </a>
       <a name="idm46045055702336">
       </a>
       <p>
        <b>
         A.10.35.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Can I run two data nodes on a single host? Two SQL nodes?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        Yes, it is possible to do this. In the case of multiple data
        nodes, it is advisable (but not required) for each node to use a
        different data directory. If you want to run multiple SQL nodes
        on one machine, each instance of
        <a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
         <span class="command">
          <strong>
           mysqld
          </strong>
         </span>
        </a>
        must
        use a different TCP/IP port.
       </p>
       <p>
        Running data nodes and SQL nodes together on the same host is
        possible, but you should be aware that the
        <a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
         <span class="command">
          <strong>
           ndbd
          </strong>
         </span>
        </a>
        or
        <a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
         <span class="command">
          <strong>
           ndbmtd
          </strong>
         </span>
        </a>
        processes
        may compete for memory with
        <a class="link" href="mysqld.html" title="6.3.1 mysqld — The MySQL Server">
         <span class="command">
          <strong>
           mysqld
          </strong>
         </span>
        </a>
        .
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-have-host-names-cluster">
       </a>
       <a name="idm46045055694544">
       </a>
       <p>
        <b>
         A.10.36.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Can I use host names with NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        Yes, it is possible to use DNS and DHCP for cluster hosts.
        However, if your application requires
        <span class="quote">
         “
         <span class="quote">
          five nines
         </span>
         ”
        </span>
        availability, you should use fixed (numeric) IP addresses, since
        making communication between Cluster hosts dependent on services
        such as DNS and DHCP introduces additional potential points of
        failure.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-have-ipv6-support-cluster">
       </a>
       <a name="idm46045055691824">
       </a>
       <p>
        <b>
         A.10.37.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        Does NDB Cluster support IPv6?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        IPv6 is supported for connections between SQL nodes (MySQL
        servers), but connections between all other types of NDB Cluster
        nodes must use IPv4.
       </p>
       <p>
        In practical terms, this means that you can use IPv6 for
        replication between NDB Clusters, but connections between nodes
        in the same NDB Cluster must use IPv4. For more information, see
        <a class="xref" href="mysql-cluster-replication-issues.html" title="25.7.3 Known Issues in NDB Cluster Replication">
         Section 25.7.3, “Known Issues in NDB Cluster Replication”
        </a>
        .
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-have-multiple-users-servers-cluster">
       </a>
       <a name="idm46045055688336">
       </a>
       <p>
        <b>
         A.10.38.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        How do I handle MySQL users in an NDB Cluster having multiple
        MySQL servers?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        MySQL user accounts and privileges are normally not
        automatically propagated between different MySQL servers
        accessing the same NDB Cluster. MySQL NDB Cluster provides
        support for shared and synchronized users and privileges using
        the
        <a class="link" href="privileges-provided.html#priv_ndb-stored-user">
         <code class="literal">
          NDB_STORED_USER
         </code>
        </a>
        privilege;
        see
        <a class="ulink" href="/doc/refman/5.7/en/mysql-cluster-privilege-distribution.html" target="_top">
         Distributed Privileges Using Shared Grant Tables
        </a>
        , for
        more information. You should be aware that this implementation
        was introduced in NDB 8.0, and is not compatible with the shared
        privileges mechanism employed in earlier versions of NDB
        Cluster. The older implementation is no longer supported in NDB
        8.0.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-how-continue-after-node-error">
       </a>
       <a name="idm46045055683632">
       </a>
       <p>
        <b>
         A.10.39.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        How do I continue to send queries in the event that one of the
        SQL nodes fails?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        MySQL NDB Cluster does not provide any sort of automatic
        failover between SQL nodes. Your application must be prepared to
        handle the loss of SQL nodes and to fail over between them.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-how-backup-restore-cluster">
       </a>
       <a name="idm46045055681440">
       </a>
       <p>
        <b>
         A.10.40.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        How do I back up and restore an NDB Cluster?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        You can use the NDB Cluster native backup and restore
        functionality in the NDB management client and the
        <a class="link" href="mysql-cluster-programs-ndb-restore.html" title="25.5.23 ndb_restore — Restore an NDB Cluster Backup">
         <span class="command">
          <strong>
           ndb_restore
          </strong>
         </span>
        </a>
        program. See
        <a class="xref" href="mysql-cluster-backup.html" title="25.6.8 Online Backup of NDB Cluster">
         Section 25.6.8, “Online Backup of NDB Cluster”
        </a>
        , and
        <a class="xref" href="mysql-cluster-programs-ndb-restore.html" title="25.5.23 ndb_restore — Restore an NDB Cluster Backup">
         Section 25.5.23, “ndb_restore — Restore an NDB Cluster Backup”
        </a>
        .
       </p>
       <p>
        You can also use the traditional functionality provided for this
        purpose in
        <a class="link" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
         <span class="command">
          <strong>
           mysqldump
          </strong>
         </span>
        </a>
        and the MySQL server.
        See
        <a class="xref" href="mysqldump.html" title="6.5.4 mysqldump — A Database Backup Program">
         Section 6.5.4, “mysqldump — A Database Backup Program”
        </a>
        , for more information.
       </p>
      </td>
     </tr>
     <tr class="question">
      <td align="left" valign="top">
       <a name="faq-cluster-what-angel-process">
       </a>
       <a name="idm46045055674256">
       </a>
       <p>
        <b>
         A.10.41.
        </b>
       </p>
      </td>
      <td align="left" valign="top">
       <p>
        What is an
        <span class="quote">
         “
         <span class="quote">
          angel process
         </span>
         ”
        </span>
        ?
       </p>
      </td>
     </tr>
     <tr class="answer">
      <td align="left" valign="top">
      </td>
      <td align="left" valign="top">
       <p>
        This process monitors and, if necessary, attempts to restart the
        data node process. If you check the list of active processes on
        your system after starting
        <a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
         <span class="command">
          <strong>
           ndbd
          </strong>
         </span>
        </a>
        , you can see
        that there are actually 2 processes running by that name, as
        shown here (we omit the output from
        <a class="link" href="mysql-cluster-programs-ndb-mgmd.html" title="25.5.4 ndb_mgmd — The NDB Cluster Management Server Daemon">
         <span class="command">
          <strong>
           ndb_mgmd
          </strong>
         </span>
        </a>
        and
        <a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
         <span class="command">
          <strong>
           ndbd
          </strong>
         </span>
        </a>
        for brevity):
       </p>
       <div class="copytoclipboard-wrapper">
        <pre class="programlisting language-terminal"><div class="docs-select-all right" id="sa98953940"><div class="copy-help left">Press ⌘+C to copy</div> <div class="right"><button class="clipboard-btn" title="Copy to Clipboard"><span class="icon-clipboard"></span></button></div></div><code class="language-terminal"><span class="token prompt">$&gt; </span><span class="token command">./ndb_mgmd</span>

<span class="token prompt">$&gt; </span><span class="token command">ps</span> aux | grep ndb
me      23002  0<span class="token punctuation">.</span>0  0<span class="token punctuation">.</span>0 122948  3104 ?        Ssl  14<span class="token punctuation">:</span>14   0<span class="token punctuation">:</span>00 <span class="token punctuation">.</span>/ndb_mgmd
me      23025  0<span class="token punctuation">.</span>0  0<span class="token punctuation">.</span>0   5284   820 pts/2    S+   14<span class="token punctuation">:</span>14   0<span class="token punctuation">:</span>00 grep ndb

<span class="token prompt">$&gt; </span><span class="token command">./ndbd</span> <span class="token property">-c</span> 127<span class="token punctuation">.</span>0<span class="token punctuation">.</span>0<span class="token punctuation">.</span>1 <span class="token property">--initial</span>

<span class="token prompt">$&gt; </span><span class="token command">ps</span> aux | grep ndb
me      23002  0<span class="token punctuation">.</span>0  0<span class="token punctuation">.</span>0 123080  3356 ?        Ssl  14<span class="token punctuation">:</span>14   0<span class="token punctuation">:</span>00 <span class="token punctuation">.</span>/ndb_mgmd
me      23096  0<span class="token punctuation">.</span>0  0<span class="token punctuation">.</span>0  35876  2036 ?        Ss   14<span class="token punctuation">:</span>14   0<span class="token punctuation">:</span>00 <span class="token punctuation">.</span>/ndbmtd <span class="token property">-c</span> 127<span class="token punctuation">.</span>0<span class="token punctuation">.</span>0<span class="token punctuation">.</span>1 <span class="token property">--initial</span>
me      23097  1<span class="token punctuation">.</span>0  2<span class="token punctuation">.</span>4 524116 91096 ?        Sl   14<span class="token punctuation">:</span>14   0<span class="token punctuation">:</span>00 <span class="token punctuation">.</span>/ndbmtd <span class="token property">-c</span> 127<span class="token punctuation">.</span>0<span class="token punctuation">.</span>0<span class="token punctuation">.</span>1 <span class="token property">--initial</span>
me      23168  0<span class="token punctuation">.</span>0  0<span class="token punctuation">.</span>0   5284   812 pts/2    R+   14<span class="token punctuation">:</span>15   0<span class="token punctuation">:</span>00 grep ndb</code></pre>
       </div>
       <p>
        The
        <a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
         <span class="command">
          <strong>
           ndbd
          </strong>
         </span>
        </a>
        process showing
        <code class="literal">
         0.0
        </code>
        for both memory and CPU usage is the
        angel process (although it actually does use a very small amount
        of each). This process merely checks to see if the main
        <a class="link" href="mysql-cluster-programs-ndbd.html" title="25.5.1 ndbd — The NDB Cluster Data Node Daemon">
         <span class="command">
          <strong>
           ndbd
          </strong>
         </span>
        </a>
        or
        <a class="link" href="mysql-cluster-programs-ndbmtd.html" title="25.5.3 ndbmtd — The NDB Cluster Data Node Daemon (Multi-Threaded)">
         <span class="command">
          <strong>
           ndbmtd
          </strong>
         </span>
        </a>
        process
        (the primary data node process which actually handles the data)
        is running. If permitted to do so (for example, if the
        <a class="link" href="mysql-cluster-ndbd-definition.html#ndbparam-ndbd-stoponerror">
         <code class="literal">
          StopOnError
         </code>
        </a>
        configuration parameter is set to
        <code class="literal">
         false
        </code>
        ), the
        angel process tries to restart the primary data node process.
       </p>
      </td>
     </tr>
    </tbody>
   </table>
  </div>
 </div>
 <br/>
</div>
