Re: Getting starnge memory error

From:
Patricia Shanahan <pats@acm.org>
Newsgroups:
comp.lang.java.programmer
Date:
Sat, 20 Jun 2009 08:50:58 -0700
Message-ID:
<VYGdnVP6-rz3mKDXnZ2dnUVZ_gidnZ2d@earthlink.com>
zigzagdna wrote:

On Jun 20, 8:55 am, Patricia Shanahan <p...@acm.org> wrote:

John B. Matthews wrote:

In article
<262e7a48-0cdd-4ba2-8f91-1142e540e...@r13g2000vbr.googlegroups.com>,
 zigzagdna <zigzag...@yahoo.com> wrote:

...

I am coming to conclusion that java is 32 bit and the limitation of
2GB or so applies to all jvm combined and not just single jvm. So
even if HP UNIX is 64 BIT and my box has 24 GB memory, to all jvm's
on that server only 2GB of heap memory available; so all the extra
memory is worthless.

I am unable to reproduce this. All my JVMs appear to be separate. Is
this a widely seen limitation?

It certainly does not apply on WindowsXP - at the time I was writing one
of my messages in this thread, I had 12 jobs, each with -Xmx700m,
running on a 32 bit JVM.

Although I don't have access to a suitable system to retest it, I
believe I have done similar things on large memory Sparc Solaris systems
using 32 bit JVMs. For example, I've used a 64 processor system to run
60 large Java CPU-bound jobs in parallel (I was required to leave a few
processors free for another users). I've never had problems related to
the total memory of all Java jobs, just the memory of an individual job.

Patricia


1. Keep in mind -Xmx is the maximum memory which process can have not
necssarily the memory used by the heap. You should have done a test
with -Xms700M -Xmx700M so process is taking that much memory when it
starts.


The jobs are a working application, not a special test for this problem.
They get the -Xmx700m because they need it. They run out of heap if I
use a lower maximum. I could not run two of them on a 1 GB system
without getting into memory thrashing - I tried. 12 run comfortably with
8 GB memory. 16 at a time have a lower throughput than 12.

Patricia

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