Playing with JVM / Java Heap Size.
- By Viral Patel on January 12, 2009
Java programs executes in JVM uses Heap of memory to manage the data. If your Java program requires a large amount of memory, it is possible that the virtual machine will begin to throw OutOfMemoryError instances when attempting to instantiate an object. The default heap size if 1 MB and can increase as much as 16 MB.
Setting/Increase JVM heap size
It is possible to increase heap size allocated by the Java Virtual Machine (JVM) by using command line options.
Following are few options available to change Heap Size.
-Xms<size> set initial Java heap size -Xmx<size> set maximum Java heap size -Xss<size> set java thread stack size
For example, you can set minimum heap to 64 MB and maximum heap 256 MB for a Java program HelloWorld.
java -Xms64m -Xmx256m HelloWorld
Getting / Reading default heap size
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);
}
}
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thank you
to set hep size in tomcat http://hiox.org/index.php?id=443
Thanks a lot
-anika
is there a way to set heap size permanently?
No. There is no way to set heap size permanently. But we use eclipse just pass the arguments like -Xmx ..
one simple way is to write a bat file to set permanently:
we can write a bat file which opens the required jar file with proper heap size settings. For example :
java -Xms64m -Xmx256m HelloWorld
this can be put in a bat file.
Im doing the bat file but I have a problem I have the .exe file… not the class
I any wat to do it whit the .bat?
or another way to set it?
I don;t know if its possible in java code to change it
hi my friends, well I tried to increase java heap space using run configuration in eclipse and netbeans, and the result was same ,I had NoClassDefFoundError , and when I deleted the command line (java -Xms64m -Xmx256m) and run the application again it worked normally except of course the pb of OutOfMemory exception, and even try dos prompt ,the vm didn’t recognize the option -Xmx and sometimes it just throw the excption NoClassDefFoundError,well it ‘s really weird thing and I don’t know how to explain it ,so little help will be nice.
Hi All,
How to check what is teh heap size in a windows machine in command line?
same error bt solution not working……!
You can read about different parts of the heap on the following link:
http://java-espresso.blogspot.com/2011/05/heap-structure-in-jvm.html
Gist of the article is below:
Following are the parts in JVM heap:
Young Generation
Eden Space
Survivor space
Virtual space
Tenured (Old) generation:
Virtual Space
Other Areas: Not a part of heap:
PermGen Area
Native Area
you can read different parts of the heap on the following link:
http://java-espresso.blogspot.com/2011/05/heap-structure-in-jvm.html
Gist of the article is below:
Following are the parts in JVM heap:
Young Generation
Eden Space
Survivor space
Virtual space
Tenured (Old) generation:
Virtual Space
Other Areas: Not a part of heap:
PermGen Area
Native Area
http://viralpatel.net/blogs/2009/01/jvm-java-increase-heap-size-setting-heap-size-jvm-heap.html
http://hausheer.osola.com/docs/5
http://www.codemiles.com/java/here-how-to-increase-java-heap-size-t663.html
HI
I tried to increase the java heap size I used this command line:
java -Xmx1K
I have this error :
error occurred during initialization of VM
could not reserve enough space for object heap
could not create the java virtual machine
I search and found the reason of this error is Heap size is larger than my computer’s physical memory , and I don’t know if it the real reason is the physical memory , can any one help my to fixed this error .
I think it is not the real reason
bye
There is a way to set this permanantly. In windows, go to control panel, click java, go to java tab, click view, and under runtime parameters put -Xmx4G or whatever size you want
In Windows you should write it as;
java -Xms64m -Xmx1024m -jar MyProgram.jar
java -Xms64m -Xmx256m HelloWorld doesn’t work for me, I added -jar part and it works now.
I need to ‘increase java heap size in jvmcfg.ini’ I have no idea what this means but from the information above see I need to ‘Xmx set maximum Java heap size’, what does that mean I actually do? Cut and past that somewhere?
I have a macbook and am not down with computer lingo so would really love some basic straightforward instruction for dummies.