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From "J. Ryan Earl" <>
Subject Re: [OT] How much RAM can java use
Date Thu, 06 Oct 2005 18:21:26 GMT
Leon Rosenberg wrote:

>Debian 3.1, kernel 2.6.x-smp (32 bit)
>Debian 3.1, kernel 2.6.x-smp-emt64 (64 bit)
>Hardware: AMD Opteron and Xeon64 (both 64 bit)
>SUN jdk1.5 and/or jdk1.4.2
>4 GB total RAM for 32-bit linux, with 3/1 memory partitioning
>16GB total RAM for 64-bit linux.
I've tested 32/64 bit JVMs extensively and done considerable amount of 
JAVA_OPTS tuning for my company's application.  On a 32-bit machine you 
can't reliably go above a -Xms=1600m without getting OOM errors.  With a 
3/1 split your virtual page table size for the entire JVM process must 
be below 3GB total virtual memory.  That's 3GB allocated, not commited.  
The JVM allocates a lot more memory besides the heap.

With the 64-bit JVMs, the sky's the limit, however the 64-bit address 
also make your application take up more space relative to a 32-bit JVM.  
A 3.2GB 64-bit heap space isn't going to double the amount of identical 
objects you can create as compared to a 32-bit 1.6GB heap space because 
all pointer references will occupy twice the space.


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