When you start an execution group, it creates a JVM for executing a Java user-defined plug-in node. You can pass parameters to the JVM to set the minimum and maximum heap sizes. To give more capacity to a message flow that is going to process large messages, reduce the minimum JVM heap size to allow the main memory heap to occupy more address space.
You do not need to increase the maximum heap size unless you use Java intensively with, for example, plug-ins or XMLTransformation nodes.
Use caution when you set the maximum heap size because the Java Runtime Environment takes the values for its initial, maximum, and current heap sizes to calculate how frequently it drives garbage collection. A large maximum heap size drives garbage collection less frequently. If garbage collection is driven less frequently, the DataFlowEngine heap size continues to grow.