Configuration of the JVM settings is different for a managed domain and a standalone server. In a managed domain, the domain controller components are responsible for starting and stoping server processes and hence determine the JVM settings. For a standalone server, it's the responsibility of the process that started the server (e.g. passing them as command line arguments).
Managed Domain
In a managed domain the JVM settings can be declared at different scopes: For a specific server group, for a host or for a particular server. If not declared, the settings are inherited from the parent scope. This allows you to customize or extend the JVM settings within every layer.
Let's take a look at the JVM declaration for a server group:
<server-groups>
<server-group name="main-server-group" profile="default">
<jvm name="default">
<heap size="64m" max-size="512m"/>
</jvm>
<socket-binding-group ref="standard-sockets"/>
</server-group>
<server-group name="other-server-group" profile="default">
<jvm name="default">
<heap size="64m" max-size="512m"/>
</jvm>
<socket-binding-group ref="standard-sockets"/>
</server-group>
</server-groups>
(See domain/configuration/domain.xml)
In this example the server group "main-server-group" declares a heap size of 64m and a maximum heap size of 512m. Any server that belongs to this group will inherit these settings. You can change these settings for the group as a whole, or a specific server or host:
<servers>
<server name="server-one" group="main-server-group" auto-start="true">
<jvm name="default"/>
</server>
<server name="server-two" group="main-server-group" auto-start="true">
<jvm name="default">
<heap size="64m" max-size="256m"/>
</jvm>
<socket-binding-group ref="standard-sockets" port-offset="150"/>
</server>
<server name="server-three" group="other-server-group" auto-start="false">
<socket-binding-group ref="standard-sockets" port-offset="250"/>
</server>
</servers>
(See domain/configuration/host.xml)
In this case, server-two, belongs to the main-server-group and inherits the JVM settings named default, but declares a lower maximum heap size.
[domain@localhost:9999 /] /host=local/server-config=server-two/jvm=default:read-resource
{
"outcome" => "success",
"result" => {
"heap-size" => "64m",
"max-heap-size" => "256m",
}
}
Standalone Server
For a standalone sever you have to pass in the JVM settings either as command line arguments when executing the $JBOSS_HOME/bin/standalone.sh script, or by declaring them in $JBOSS_HOME/bin/standalone.conf. (For Windows users, the script to execute is %JBOSS_HOME%/bin/standalone.bat while the JVM settings can be declared in %JBOSS_HOME%/bin/standalone.conf.bat.)