99 lines
6.8 KiB
HTML
99 lines
6.8 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<META http-equiv="Content-Type" content="text/html; charset=utf-8">
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<LINK rel="stylesheet" type="text/css" href="../../../rzahg/ic.css">
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<title>Java virtual machine tuning parameters</title>
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</head>
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<BODY>
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<!-- Java sync-link -->
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<SCRIPT LANGUAGE="Javascript" SRC="../../../rzahg/synch.js" TYPE="text/javascript"></SCRIPT>
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<h4><a name="prftunejvm"></a>Java virtual machine tuning parameters</h4>
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<p>Because the application server is a Java process, it requires a Java virtual machine (JVM) to run, and to support the Java applications running on it. For more information about JVM settings, see <a href="help/urun_rconfproc_jvm.html">Java virtual machine settings</a>. <img src="help.gif" width="18" height="15" alt="Go to Help documentation"></p>
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<p>For additional tuning information, see <a href="prftunejmem.htm">Java memory tuning tips</a>. If your application experiences slow response times at startup or first touch, you may want to consider using the Java user classloader cache. For more information, see <a href="../program/clscache.htm">Java cache for user classloaders</a> in the <em>Programming</em> topic.</p>
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<p>You can adjust these settings that determine how the system uses the JVM:</p>
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<ul>
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<li><strong>Class garbage collection (-Xnoclassgc)</strong>
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<ul>
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<li>Description: This argument disables class garbage collection so that your applications can reuse classes more easily. You can monitor garbage collection using the -verbosegc configuration setting because its output includes class garbage collection statistics.</li>
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<li>How to view or set:
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<ol>
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<li><a href="acstart.htm">Start the administrative console</a>.</li>
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<li>In the topology tree, expand <strong>Servers</strong> and click <strong>Application Servers</strong>.</li>
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<li>Click the name of the application server that you want to configure.</li>
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<li>Click <strong>Process Definition</strong>.</li>
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<li>On the <strong>Process Definition</strong> page, click <strong>Java Virtual Machine</strong>.</li>
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<li>In the <strong>Generic JVM arguments</strong> field, type <tt>-Xnoclassgc</tt>.</li>
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<li>Click <strong>Apply</strong> or <strong>OK</strong>.</li>
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<li><a href="acsave.htm">Save the configuration</a>.</li>
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<li>Stop and restart the application server.</li>
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</ol></li>
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<li>Default value: By default, class garbage collection is enabled.</li>
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<li>Recommended value: Do not disable class garbage collection.</li>
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</ul><p></p></li>
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<li><strong><a name="heap"></a>Initial heap size</strong>
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<ul>
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<li>Description: The initial heap size specifies how often garbage collection runs, and can have a significant effect on performance. For more information, see <a href="http://www-1.ibm.com/servers/eserver/iseries/perfmgmt/pdf/tuninggc.pdf" target="_blank">Tuning Garbage Collection for Java<sup>(TM)</sup> and WebSphere on iSeries</a>. <img src="www.gif" width="18" height="15" alt="Link outside Information Center" border="0"></li>
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<li>How to view or set:
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<ol>
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<li><a href="acstart.htm">Start the administrative console</a>.</li>
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<li>In the topology tree, expand <strong>Servers</strong> and click <strong>Application Servers</strong>.</li>
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<li>Click the name of the application server that you want to configure.</li>
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<li>Click <strong>Process Definition</strong>.</li>
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<li>On the <strong>Process Definition</strong> page, click <strong>Java Virtual Machine</strong>.</li>
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<li>In the <strong>Initial Heap Size</strong> field, specify a value.</li>
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<li>Click <strong>Apply</strong> or <strong>OK</strong>.</li>
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<li><a href="acsave.htm">Save the configuration</a>.</li>
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<li>Stop and restart the application server.</li>
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</ol></li>
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<li>Default value: For iSeries, the default value is 96.</li>
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<li>Recommended value: 96MB per processor</li>
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</ul><p></p></li>
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<li><strong>Maximum heap size</strong>
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<ul>
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<li>Description: This parameter specifies the maximum heap size available to the JVM code, in megabytes.</li>
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<li>How to view or set:
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<ol>
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<li><a href="acstart.htm">Start the administrative console</a>.</li>
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<li>In the topology tree, expand <strong>Servers</strong> and click <strong>Application Servers</strong>.</li>
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<li>Click the name of the application server that you want to configure.</li>
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<li>Click <strong>Process Definition</strong>.</li>
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<li>On the <strong>Process Definition</strong> page, click <strong>Java Virtual Machine</strong>.</li>
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<li>The value is displayed in the <strong>Maximum Heap Size</strong> field.</li>
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<li>Click <strong>Apply</strong> or <strong>OK</strong>.</li>
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<li><a href="acsave.htm">Save the configuration</a>.</li>
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<li>Stop and restart the application server.</li>
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</ol></li>
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<li>Default value: For iSeries, the default value is 0. A value of 0 specifies that there is no maximum value.</li>
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<li>Recommended value: It is recommended that you do not change the maximum heap size. When the maximum heap size triggers a garbage collection cycle, the iSeries JVM's garbage collection stops operating asynchronously. As a result, the application server cannot process user threads until the garbage collection cycle ends, and performance is significantly lower.</li>
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</ul><p></p></li>
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<li><strong>Just-In-Time (JIT) compiler</strong>
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<ul>
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<li>Description: A Just-In-Time (JIT) compiler is a platform-specific compiler that generates machine instructions for each method as needed. For more information, see <a href=" ../../../rzaha/runtperf.htm#usingthejustintimecompiler">Using the Just-In-Time compiler</a> and <a href="../../../rzaha/jit.htm">Just-In-Time compiler</a> in the <em>IBM Developer Kit for Java</em> topic.</li>
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<li>How to view or set:
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<ol>
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<li><a href="acstart.htm">Start the administrative console</a>.</li>
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<li>In the topology tree, expand <strong>Servers</strong> and click <strong>Application Servers</strong>.</li>
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<li>Click the name of the application server that you want to configure.</li>
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<li>Click <strong>Process Definition</strong>.</li>
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<li>On the <strong>Process Definition</strong> page, click <strong>Java Virtual Machine</strong>.</li>
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<li>If you want to disable JIT, select the checkbox for <strong>Disable JIT</strong>.</li>
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<li>Click <strong>Apply</strong> or <strong>OK</strong>.</li>
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<li><a href="acsave.htm">Save the configuration</a>.</li>
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<li>Stop and restart the application server.</li>
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</ol></li>
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<li>Default value: By default, JIT is enabled.</li>
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<li>Recommended value: It is recommended that you do not disable the JIT compiler. The os400.jit.mmi.threshold can have a significant effect on performance. For more information about the JIT compiler and the os400.jit.mmi.threshold property, see <a href="../../../rzaha/jit.htm">Just-In-Time compiler</a> in the <em>IBM Developer Kit for Java</em> topic.</li>
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</ul></li>
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</ul>
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</body>
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</html>
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