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From Alan Chaney <>
Subject Re: what is the upper limit of maximum heap memory for Tomcat with 32-bit JVM running on Red Hat Linux 4 (32-bit)
Date Thu, 23 Jul 2009 23:30:01 GMT
You are using a 32 bit operating system and a 32 bit processor. To make 
more than 4GB of ram available you must ensure that you have PAE support 
enabled in your kernel (search Google for Physical Address Extension) 
which may mean re-compiling for RHEL 4 (see Red Hat). Your processor may 
not support it but I'd suspect that when you say 4 processors you 
probably mean 4 cores and I believe all 4 core Intel CPUs do support 
PAE. Re-reading your email I see that you say that you have 4.5G of free 
memory - how did you determine this? 'top'?

Even so, I cannot find any clear statement on the web that the 32 bit 
JRE will be able to address more than 4G even if you do have PAE 
enabled. I suspect not. Actually, 'suspect' is way too mild a term ... I 
would be completely astounded if you could...

Possible workarounds are:

1. Try running 2 JVMs ( when you have PAE enabled) - of course this may 
not work in your application (you'd have to have two Tomcat instances.)

2. Your other 'workaround' is to install a 64 bit OS and a 64 bit JVM. 
Then you can have 7G+ for the JVM.


Alan Chaney

Li,Henry wrote:
> My Tomcat is running on 32-bit Red Hat 4 (2.6.9-78.0.1.ELsmp), host server has 8G physical
memory and 4 processors.
>  java version "1.4.2"  gcj (GCC) 3.4.6 20060404 (Red Hat 3.4.6-10)
> I got java.lang.OutOfMemoryError
> Current configuration: -Xms1024M -Xmx2304M
> The host server has about 4.5G free memory. When I tried to increase -Xmx2304M to -Xmx3000M,
I got this error:
> Error occurred during initialization of VM, Could not reserve enough space for object
> The maximum # I can reach is -Xmx2680M.
> QUESTION: Is there an upper limit for -Xmx? What is the work around? How can I use my
free memory on the server to
> get rid of the OutOfMemoryError?
> Thanks,
> Henry
> !DSPAM:4a68ee3b41041381456296!

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