Monday, December 04, 2006

MAX Memory For Your JVM

There is an interesting discussion going on the Java Posse Google Group on the maximum memory that can be allocated to a JVM.

Now if you are running a 32-bit system, then 4 GB is the maximum addressable memory. Of this, the OS (Windows)  takes about 2 GB (though it can be tweaked to take less according to a post on the Java forum), leaving 2 GB for your apps. You could theoretically assign this 2 GB to your JVM, but thread stacks are allocated memory outside of the JVM. So if your application uses a lot of threads, you will have to leave some space for the thread stacks.

Now if you use a 64-bit system, then you can allocate a LOT more memory to your JVM, but to do this your entire stack (CPU, OS, JVM, any other dependencies) needs to be 64-bit compliant. 

If you want an unlimited heap size for your JVM, you might want to check out Azul. John Reynolds wrote an interesting blog on scaling JVM's with Azul. 

By the way of you enjoy listening to podcasts and are into Java, then you absolutely must listen to the JavaPosse podcast. It is very informative and entertaining.



Notes: This text was originally posted on my earlier blog at http://www.adaptivelearningonline.net
Here are the comments from the original post

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COMMENT:
AUTHOR: Amish
EMAIL:
URL:
DATE: 01/17/2007 10:00:39 PM
hey.. sourceforge has serverfarm which they share with developers to work on it. You might be able to try various hardware available with them to check performance of systems and jvms...

COMMENT:
AUTHOR: Parag
DATE: 01/18/2007 05:30:14 PM
Hey Amish,
Good to hear from you. That is a good idea to check for peformance.

I will checkup with them for access, meanwhile, do you know if we need to apply or we can just create an account somewhere and start using their servers?

--
Parag

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