About Pierre Hugues Charbonneau

Pierre-Hugues Charbonneau (nickname P-H) is working for CGI Inc. Canada for the last 10 years as a senior IT consultant. His primary area of expertise is Java EE, middleware & JVM technologies. He is a specialist in production system troubleshooting, root cause analysis, middleware, JVM tuning, scalability and capacity improvement; including internal processes improvement for IT support teams. P-H is the principal author at Java EE Support Patterns.

Java Heap Space – JRockit and IBM VM

This article will provide you with an overview of the JRockit Java Heap Space vs. the HotSpot VM. It will also provide you some background on Oracle future plans regarding JRockit & HotSpot.

Oracle JRockit VM Java Heap: 2 different memory spaces
 -The Java Heap (YoungGen and OldGen)
 -The Native memory space (Classes pool, C-Heap, Threads…)

Where is the PermGen space?

Similar to the IBM VM, there is no PermGen space for the JRockit VM. The PermGen space is only applicable to the HotSpot VM. The JRockit VM is using the Native Heap for Class metadata related data. Also, as you probably saw from my other article, Oracle Sun is also starting to remove the PermGen space for the HotSpot VM.

Why is the JRockit VM Java process using more memory than HotSpot VM?

The JRockit VM tend to uses more native memory in exchange for better performance. JRockit does not have an interpretation mode, compilation only, so due to its additional native memory needs the process size tends to use a couple of hundred MB larger than the equivalent Sun JVM size. This should not be a big problem unless you are using a 32-bit JRockit with a large Java Heap requirement; in this scenario, the risk of OutOfMemoryError due to Native Heap depletion is higher for a JRockit VM (e.g. for a 32-bit VM, bigger is the Java Heap, smaller is memory left for the Native Heap).

What is Oracle’s plan for JRockit?

Current Oracle JVM strategy is to merge both HotSpot and JRockit product lines to a single JVM project that will include the best features of each VM. This will also simplify JVM tuning since right now failure to understand the differences between these 2 VM’s can lead to bad tuning recommendations and performance problems.
Please feel free to post any comment or question on the JRockit VM.

Java Heap Space – IBM VM

This short article will provide you with a high level overview of the different Java memory spaces for the IBM VM.

This understanding is quite important given the implementation & naming convention differences between HotSpot & IBM VM.

IBM VM: 2 different memory spaces

The IBM VM memory is split between 2 memory spaces:
- The Java Heap (nursery and tenured spaces)
- The Native Heap (C-Heap)

Where is the PermGen space?

This is by far the most typical question I get from Java EE support individuals supporting an IBM VM environment for this first time. The answer: there is no PermGen space for the IBM VM. The PermGen space is only applicable to the HotSpot VM. The IBM VM is using the Native Heap for Class metadata related data. Also, as you probably saw from my other article, Oracle / Sun is also starting to remove the PermGen space for the HotSpot VM.

The next article will provide you a tutorial on how to enable and analyze verbose GC for an IBM VM. Please feel free to post any comment or question on the IBM VM.

Reference: Java Heap Space – JRockit VM and Java Heap Space – IBM VM from our JCG partner Pierre-Hugues Charbonneauat at the Java EE Support Patterns & Java Tutorialblog.

Do you want to know how to develop your skillset to become a Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you two of our best selling eBooks for FREE!

JPA Mini Book

Learn how to leverage the power of JPA in order to create robust and flexible Java applications. With this Mini Book, you will get introduced to JPA and smoothly transition to more advanced concepts.

JVM Troubleshooting Guide

The Java virtual machine is really the foundation of any Java EE platform. Learn how to master it with this advanced guide!

Given email address is already subscribed, thank you!
Oops. Something went wrong. Please try again later.
Please provide a valid email address.
Thank you, your sign-up request was successful! Please check your e-mail inbox.
Please complete the CAPTCHA.
Please fill in the required fields.

Leave a Reply


− 5 = one



Java Code Geeks and all content copyright © 2010-2014, Exelixis Media Ltd | Terms of Use | Privacy Policy
All trademarks and registered trademarks appearing on Java Code Geeks are the property of their respective owners.
Java is a trademark or registered trademark of Oracle Corporation in the United States and other countries.
Java Code Geeks is not connected to Oracle Corporation and is not sponsored by Oracle Corporation.
Do you want to know how to develop your skillset and become a ...
Java Rockstar?

Subscribe to our newsletter to start Rocking right now!

To get you started we give you two of our best selling eBooks for FREE!

Get ready to Rock!
You can download the complementary eBooks using the links below:
Close