JVM Configuration


This page explains how to configure runtime settings for XAP.NET applications. In general, the development phase of a XAP.NET based application does not require runtime tuning settings as the defaults are usually satisfactory. In later testing and production phases, however, it is sometimes required to customize the default configuration.

Jvm Location

GigaSpaces XAP.NET is bundled with Oracle Java SE 8 update 121, aiming to save .NET users the hassle of downloading and installing Java. However, it is quite simple to bind it to a different JVM (For a list of supported JVMs refer to Supported Platforms in the release notes):

  1. Edit the Settings.xml file (located in <XapNet>\config\Settings.xml).
  2. Locate the <XapNet.Runtime.JavaHome> node and change its value to the location of the JVM you wish to use.
Using JAVA_HOME

Many systems define an environment variable called JAVA_HOME which points to the JVM installation, since most java applications and libraries (including GigaSpaces XAP) use JAVA_HOME to locate java. Since the Settings.xml file supports environment variable expansion, it is possible to set to %JAVA_HOME%, so you can later on change the jvm location without editing the xml file.

Jvm Settings

Unlike .NET applications, which are compiled to executable files, java applications are compiled to .class or .jar files which are executed using the Java Application Launcher (java.exe) tool. This tool supports various options which control the way the application is executed, such as memory allocation, garbage collection and more.

XAP.NET tools and applications use Java Native Interface (JNI) instead of java.exe to launch the JVM and execute java code, and use the Application Configuration File to load JVM settings.

To configure JVM settings, add a GigaSpaces section to the application configuration file:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
   <configSections>
      <section name="GigaSpaces" type="GigaSpaces.Core.Configuration.GigaSpacesCoreConfiguration, GigaSpaces.Core"/>
   </configSections>
   <GigaSpaces>
      <JvmSettings>
         <!-- Jvm Settings -->
      </JvmSettings>
   </GigaSpaces>
</configuration>

The rest of this section explains and demonstrates the various JVM settings.

JvmCustomOptions

The JvmCustomOptions section accepts a collection of custom options, similar to java.exe options. For example, this

java.exe -XX:+AggressiveOpts

is equivalent to

<JvmSettings>
   <JvmCustomOptions>
      <add Option="-XX:+AggressiveOpts"/>
   </JvmCustomOptions>
</JvmSettings>

This element also has an attribute called IgnoreUnrecognized, which determines the behavior when an unrecognized option is encountered: true means ignore that option, false means throw an exception and abort. The default is false.

In general, this section provides equivalent functionality to java.exe and thus is sufficient. However, since most .NET users are not familiar with common java options, The XAP.NET JVM settings schema provides additional elements which act as aliases and are more readable to non-java users.

JvmDll

The java.exe tool supports two mutually exclusive modes, called -client and -server, which determine what VM will be loaded. In fact, client and server are different implementations of the JVM residing in two separate jvm.dll files.

This option cannot be configured in JvmCustomOptions because it is not supported by JNI. Instead, JvmDll comes to the rescue. For example, this

java.exe -server

is equivalent to

<JvmSettings>
   <JvmDll Mode="Server"/>
</JvmSettings>

the Mode attribute can be either Client, Server or Custom. If Mode is set to Client or Server, the <XapNet.Runtime.JavaHome> (explained in Jvm Lovation]) is used to locate the java home, and either the client or server VM is selected according to the mode. If Mode is set to Custom, the <XapNet.Runtime.JavaHome> is ignored, and the location of the jvm is determined by a Path attribute. for example:

<JvmSettings>
   <JvmDll Mode="Custom" Path="C:\Foo\MyJvm.dll"/>
</JvmSettings>

JvmMemory

java.exe provides two options to control memory allocation: -Xms determines the initial heap size, and -Xms determines the maximum heap size. The JvmSettings section offers an alias section called JvmMemory. For example:

<JvmSettings>
   <JvmCustomOptions>
      <add Option="-Xms512m"/>
      <add Option="-Xmx1024m"/>
   </JvmCustomOptions>
   <!-- is equivalent to -->
   <JvmMemory InitialHeapSizeInMB="512" MaximumHeapSizeInMB="1024"/>
</JvmSettings>

Note: It is not recommended to define memory settings both as custom options and in the JvmMemory section, since the expected behavior is not clear.

JvmClassPath

The class path is the path that Java searches for classes and other resource files. It is usually specified as a semicolon-separated list of paths. The JvmSettings offers a more readable solution in the form of JvmClassPath. The following examples are equivalent:

java.exe -classpath C:\Foo;C:\Bar
java.exe -Djava.class.path=C:\Foo;C:\Bar
<JvmSettings>
   <JvmCustomOptions>
      <add Option="-Djava.class.path=C:\Foo;C:\Bar"/>
   </JvmCustomOptions>
</JvmSettings>
<JvmSettings>
   <JvmClassPath>
      <add Path="C:\Foo"/>
      <add Path="C:\Bar"/>
   </JvmClassPath>
</JvmSettings>

In addition to being more readable, the JvmClassPath has another perk: it supports wildcard-expansion. So, for example, we could specify C:\Foo\*.jar and it will be expanded to include all jar files in C:\Foo before being passed to java.

JvmBootClassPath

Similar to the class path, which determines the location of user classes, the boot class path determines the location of java bootstrap classes. The JvmSettings offers a more readable solution in the form of JvmBootClassPath, similar to JvmClassPath. The following examples are equivalent:

java.exe -Xbootclasspath/p:C:\Foo;C:\Bar
<JvmSettings>
   <JvmCustomOptions>
      <add Option="-Xbootclasspath/p:C:\Foo;C:\Bar"/>
   </JvmCustomOptions>
</JvmSettings>
<JvmSettings>
   <JvmBootClassPath>
      <add Path="C:\Foo"/>
      <add Path="C:\Bar"/>
   </JvmBootClassPath>
</JvmSettings>

Note that this alias is used to prepend boot class path (/p). java.exe also supports -Xbootclasspath/a, which is used to append boot class path. There’s no alias for that in JvmSettings, but of course it can be used in the JvmCustomOptions.

JvmBootClassPath supports wildcard expansion, similar to JvmClassPath.