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<b>Oracle9<em>i</em> Administrator's Reference </b>
<br />
<b>Release 2 (9.2.0.1.0) for UNIX Systems: AIX-Based Systems, Compaq Tru64 UNIX, HP 9000 Series HP-UX, Linux Intel, and Sun Solaris</b>
<br />
Part No. A97297-01
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<h1>
<font face="arial, helvetica, sans-serif" color="#330099">F
<br /> Oracle Cluster Management Software <br />for Linux
</font>
</h1>
<p>Oracle Cluster Management Software (OCMS) is available with Oracle9<em>i</em> on Linux systems. This appendix contains the following sections:
</p>
<ul>
<li type="disc">
<p><a href="#i632957"><em></em>Overview</a>
</p>
</li>
<li type="disc">
<p><a href="#i639634">Watchdog Daemon</a>
</p>
</li>
<li type="disc">
<p><a href="#i638962">Cluster Manager</a>
</p>
</li>
<li type="disc">
<p><a href="#i633044">Starting OCMS</a>
</p>
</li>
<li type="disc">
<p><a href="#i634995">Watchdog Daemon and Cluster Manager Starting Options</a>
</p>
</li>
</ul><a id="i632957" name="i632957"></a>
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<h2>
<font face="arial, helvetica, sans-serif" color="#330099"><em></em>Overview
</font>
</h2>
<p>OCMS is included with the Oracle9<em>i</em> Enterprise Edition for Linux. It provides cluster membership services, a global view of clusters, node monitoring, and cluster reconfiguration. It is a component of Oracle9<em>i</em> Real Application Clusters on Linux and is installed automatically when you choose Oracle9<em>i</em> Real Application Clusters. OCMS consists of the following components:
</p>
<ul>
<li type="disc">
<p>Watchdog Daemon
</p>
</li>
<li type="disc">
<p>Cluster Manager
</p>
</li>
</ul>
<p><a href="#CHDBFHJJ">Figure F-1</a> shows how the Watchdog daemon provides services to the Cluster Manager.
</p><a id="CHDBFHJJ" name="CHDBFHJJ"></a><a id="sthref765" name="sthref765"></a>
<div class="figure">
<p><strong><em><font face="arial, helvetica, sans-serif">Figure F-1 Oracle Instance and Components of OCMS
</font></em></strong>
</p>
</div class="figure">
<img src="./img/watchdog.jpg" alt="This graphic shows the components of OCMS.">
<br />
</div class="sect1"><a id="i639634" name="i639634"></a>
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<h2>
<font face="arial, helvetica, sans-serif" color="#330099">Watchdog Daemon<a id="sthref767" name="sthref767"></a><a id="sthref768" name="sthref768"></a>
</font>
</h2>
<p>The Watchdog daemon (<code>watchdogd</code>) uses a software-implemented Watchdog timer to monitor selected system resources to prevent database corruption.Watchdog timer is a feature of the Linux kernel. The Watchdog daemon is part of Oracle9<em>i</em> Real Application Clusters.
</p>
<p>The Watchdog daemon monitors the Cluster Manager and passes notifications to the Watchdog timer at defined intervals. The behavior of the Watchdog timer is partially controlled by the <a id="sthref769" name="sthref769"></a><a id="sthref770" name="sthref770"></a>CONFIG_WATCHDOG_NOWAYOUT configuration parameter of the Linux kernel.
</p>
<p>If you use Oracle9<em>i</em> Real Application Clusters, you must set the value of the CONFIG_WATCHDOG_NOWAYOUT configuration parameter to Y. If the Watchdog Timer detects an Oracle instance or Cluster Manager failure, it resets the instance to avoid possible database corruption.
</p>
<p>For information on how to set the CONFIG_WATCHDOG_NOWAYOUT parameter, see the <code>/usr/src/linux/Documentation/configure.help</code> file in the Linux kernel source code. For more information on Watchdog devices, see the <code>/usr/src/linux/Documentation/watchdog.txt</code> file in the Linux kernel source code.
</p>
</div class="sect1"><a id="i638962" name="i638962"></a>
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<h2>
<font face="arial, helvetica, sans-serif" color="#330099">Cluster Manager
</font>
</h2>
<p>The Cluster Manager maintains the status of the nodes and the Oracle instances across the cluster. The Cluster Manager process runs on each node of the Real Applications Cluster. Each node has one Cluster Manager. The number of Oracle instances for each node is not limited by Oracle9<em>i</em> Real Application Clusters. The Cluster Manager uses the following communication channels between nodes:
</p>
<ul>
<li type="disc">
<p>Private network
</p>
</li>
<li type="disc">
<p>Quorum partition on the shared disk
</p>
</li>
</ul>
<p>During normal cluster operations, the Cluster Managers on each node of the cluster communicate with each other through heartbeat messages sent over the private network. The quorum partition is used as an emergency communication channel if a heartbeat message fails. A heartbeat message can fail for the following reasons:
</p>
<ul>
<li type="disc">
<p>The Cluster Manager terminates on a node
</p>
</li>
<li type="disc">
<p>The private network fails
</p>
</li>
<li type="disc">
<p>There is an abnormally heavy load on the node
</p>
</li>
</ul>
<p>The Cluster Manager uses the quorum partition to determine the reason for the failure. From each node, the Cluster Manager periodically updates the designated block on the quorum partition. Other nodes check the timestamp for each block. If the message from one of the nodes does not arrive, but the corresponding partition on the quorum has a current timestamp, the network path between this node and other nodes has failed.
</p>
<p>Each Oracle instance registers with the local Cluster Manager. The Cluster Manager monitors the status of local Oracle instances and propagates this information to Cluster Managers on other nodes. If the Oracle instance fails on one of the nodes, the following events occur:
</p>
<ol type="1" start="1">
<li>
<p>The Cluster Manager on the node with the failed Oracle instance informs the Watchdog daemon about the failure.
</p>
</li>
<li>
<p>The Watchdog daemon requests the Watchdog timer to reset the failed node.
</p>
</li>
<li>
<p>The Watchdog timer resets the node.
</p>
</li>
<li>
<p>The Cluster Managers on the surviving nodes inform their local Oracle instances that the failed node is removed from the cluster.
</p>
</li>
<li>
<p>Oracle instances in the surviving nodes start the Oracle9<em>i</em> Real Application Clusters reconfiguration procedure.
</p>
</li>
</ol>
<p>The nodes must reset if an Oracle instance fails. This ensures that:
</p>
<ul>
<li type="disc">
<p>No physical I/O requests to the shared disks from the failed node occur after the Oracle instance fails.
</p>
</li>
<li type="disc">
<p>Surviving nodes can start the cluster reconfiguration procedure without corrupting the data on the shared disk.
</p>
</li>
</ul>
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<p>
<font face="arial, helvetica, sans-serif">
<strong>See Also:</strong>
</font>
</p><a href="#i635111">"Configuring Timing for Cluster Reconfiguration"</a> and <a href="#i634995">"Watchdog Daemon and Cluster Manager Starting Options"</a> for more information on the Cluster Manager.
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</table><br />
</div class="sect1"><a id="i633044" name="i633044"></a>
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<h2>
<font face="arial, helvetica, sans-serif" color="#330099">Starting OCMS
</font>
</h2>
<p>The following sections describe how to start OCMS:
</p>
<ul>
<li type="disc">
<p><a href="#i638964">Starting the Watchdog Daemon</a>
</p>
</li>
<li type="disc">
<p><a href="#i638965">Configuring the Cluster Manager</a>
</p>
</li>
<li type="disc">
<p><a href="#i633352">Starting the Cluster Manager</a>
</p>
</li>
<li type="disc">
<p><a href="#i635111">Configuring Timing for Cluster Reconfiguration</a>
</p>
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<td align="left" colspan="1" rowspan="1">
<p>
<font face="arial, helvetica, sans-serif">
<strong>Note:</strong>
</font>
</p>Oracle Corporation supplies the <code>$ORACLE_HOME/oracm/bin/ocmstart.sh</code> sample startup script. Run this script as the <code>root</code> user. Make sure that the ORACLE_HOME and PATH environment variables are set as described in the <em>Oracle9i Installation Guide Release 2 (9.2.0.1.0) for UNIX Systems</em>. After you are familiar with starting the Watchdog daemon and the Cluster Manager, you can use the script to automate the start-up process.
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</li>
</ul><a id="i638964" name="i638964"></a>
<div class="sect2">
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<h3>
<font face="arial, helvetica, sans-serif" color="#330099">
Starting the Watchdog Daemon<a id="sthref774" name="sthref774"></a>
</font>
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