"Throwing OutOfMemory: class allocation" error on Linux x86-64

Question

Hi.
My system is:
4 Intel Xeon processors, 24GB RAM
OS: Fedora Core 8 2.6.23.1-42.fc8
JRockit: 4.0.1 Mission Control for 1.6.0
I try to run Apache Tomcat (via jsvc and using APR) using JRockit JVM and I get the following error: "Throwing OutOfMemory: class allocation, 766248 loaded, 768K footprint in check_alloc (classalloc.c:213) 268 bytes requested." (multiple times) and then JVM crashes.
I use following config options for JVM: -Xms3000m -Xmx4000m -Xns:800m -XXkeepAreaRatio:20 -XXgcThreads:4 -XXcompressedRefs:enable=false -XX:+UseStringCache -Xgc:gencon -Xverbose:gc -Xverbosetimestamp
I also tried to run it with different heap sizes (more than 4GB) and without -XXcompressedRefs option specified (in which case JRockit used compressed references supporting heap size up to 32GB) but nothing helps - there is the same error every time.
I suspect that it has something to do with heap size though because when I run it on different machine with only 2GB of RAM and heap size set accordingly then it runs ok. I also need it to have plenty of heap space available because it is under heavy load.
Do you have any idea what can cause such a behaviour? I'm sure that I'm not exhausting available native memory (there is 24GB on that machine and normally there is 9-12GB used by applications, mainly Oracle DB Server, and the rest is cached by OS). Also Tomcat runs ok on Sun's JVM (meaning there is no OutOfMemory errors but there are some other issues which I hoped to resolve partly by using JRockit).

Answer 1

I also thought the syntax of -XXcompressedRefs is as you wrote but in the newest JRockit version it's -XXcompressedRefs:enable=false (I found out the hard way, having to spend some time on searching it :) ). The syntax -XXcompressedRefs:false doesn't work in this version. If you're wondering if it has desirable effect: it has. As a proof, here is a snippet from log file:
"[memory ][Thu Sep 23 12:51:16 2010][28083] Running with 64 bit heap and uncompressed references.
[memory ][Thu Sep 23 12:51:16 2010][28083] GC mode: Garbage collection optimized for short pausetimes, strategy: Generational Concurrent Mark & Sweep."
About the post I didn't read this one but few on the same topic telling the same thing.
I will try later running it with -Xverbose:class later (I can't do it right away as it is a production environment I have trouble with).
The curious thing though is that on the second machine it runs ok with smaller heap size (software is identical, loads the same number of classes). So I wonder what is the way to make it work with larger heap (because I'm sure it will need it) - all the posts about this say that I should decrease heap size. Also in Sun JVMs there is an option to set PermGen size. I realize that there is no such thing in JRockit but maybe there is some setting related to memory used for storing loaded classes?
Thanks for any suggestions.
Edited by: user1562668 on Sep 23, 2010 2:46 PM