Change the Java VM Memory Limits
If you are running out of memory even though your server has a lot of RAM, you probably need to increase the resources allocated to the JRE instance that runs the Pentaho software you're trying to improve performance on. Adjusting the memory limit is an easy configuration change to make, but the instructions differ depending on the client tool or Web application server you're using. Refer only to the sections below that apply to your situation.
If you are running multiple Pentaho programs concurrently, the sum of their JVM maximum memory limits must not exceed the available RAM minus system overhead.