how to increase java heap memory permanently?

The Java Virtual Machine takes two command line arguments which set the initial and maximum heap sizes: -Xms and -Xmx. You can add a system environment variable named _JAVA_OPTIONS, and set the heap size values there.
For example if you want a 512Mb initial and 1024Mb maximum heap size you could use:

under Windows:

SET _JAVA_OPTIONS = -Xms512m -Xmx1024m

under Linux:

export _JAVA_OPTIONS="-Xms512m -Xmx1024m"

It is possible to read the default JVM heap size programmatically by using totalMemory() method of Runtime class. Use following code to read JVM heap size.

public class GetHeapSize {
    public static void main(String[]args){

        //Get the jvm heap size.
        long heapSize = Runtime.getRuntime().totalMemory();

        //Print the jvm heap size.
        System.out.println("Heap Size = " + heapSize);
    }
}

This worked for me:

export _JAVA_OPTIONS="-Xmx1g"

It's important that you have no spaces because for me it did not work. I would suggest just copying and pasting. Then I ran:

java -XshowSettings:vm

and it will tell you:

Picked up _JAVA_OPTIONS: -Xmx1g

You also use this below to expand the memory

export _JAVA_OPTIONS="-Xms512m -Xmx1024m -Xss512m -XX:MaxPermSize=1024m"

Xmx specifies the maximum memory allocation pool for a Java virtual machine (JVM)

Xms specifies the initial memory allocation pool.

Xss setting memory size of thread stack

XX:MaxPermSize: the maximum permanent generation size

if you need to increase reserved memory, there are VM parameters -Xms and -Xmx, usage e.g. -Xms512m -Xmx512m . There is also parameter -XX:MaxPermSize=256m which changes memory reserved for permanent generation

If your application runs as windows service, in Control panels -> Administration tools -> Services you can add some run parameters to your service