How to set java heap size in Glassfish Application Server?

Stop the application server, edit

$GLASSFISH_HOME/domains/domain1/config/domain.xml, search for XML element name java-config and jvm-options. For example,

<java-config suffix="...">
<jvm-options>-Xmx512m</jvm-options>
<jvm-options>-XX:NewRatio=2</jvm-options>
<jvm-options>-XX:MaxPermSize=128m</jvm-options>
...</java-config>

                                        You can also change these settings in the web-based admin console, typically at http://localhost:4848/, or https://localhost:4848/. Go to Application Server near the top of the left panel, and then on the right panel, click JVM Settings | JVM Options, and you will see a list of existing JVM options. You can add new ones and modify existing ones there.

                                Yet another option is to use its Command Line Interface (CLI) tool command, such as

./asadmin help create-jvm-options
./asadmin help delete-jvm-options

They may be a bit hard to use manually, but are well suited for automated scripts.