[TriLUG] Memory Monitor on a Redhat system

[Tim Jowers]

On 3/29/07, Robert Dale <robdale at gmail.com> wrote:
>
> On 3/29/07, Tim Jowers <timjowers at gmail.com> wrote:
> >    Ideas: One other silly but possible thing is to try to start another
> Java
> > app than JBoss. Java is not enterprise-ready yet with its mem size and
> is
> > basically limited to 3G of user space per VM so you have to run several
> > instances on large RAM machines (at least that's what a BEA consultant
> told
> > me ;-).  Also, does "sync" help to free up any space? You can also set
> > swapoff to speed up the problem or even limit the RAM during boot with a
> > kernel parameter in GRUB etc. Last of all, in BEA a few years back I saw
> a
> > mem alloc exception which was actually due to a mismatch between the AIX
>
> > system calls and the java runtime code. We just changed the Java code to
> > execute another set of system calls.
>
> Did the BEA guy say Linux isn't enterprise ready because of its memory
> limit?



Nope, I said that. Imagine if I said, "well, Linux box can only address 2GB
of your 12GB RAM".  Would that be enterprise ready?  That's just old school.
Of course one can run a 64 bit JVM and get to more RAM but Linux does allow
you to address up to 64GB with a 32bit architecture. 32-bit JVM's do not.
Why? They are a "virtual machine" so do not know about PAE. They *could* but
I guess Intel would be the one to contrib to Java. Maybe now that the JVM is
being Open Sourced one can expect that sort of innovation. I heard AMD
contrib'ed a major part of the 64 bit Linux arch code???
    But its a moot questions since the main use of Java is webapps and so
you can run several instances of your appserver on the same box and use your
clustering layer to exchange data. Out-of-process data exchange is 2 orders
of magnitude slower than in-process but still multiple orders of magnitude
faster than network exchanges so you can safely ignore the performance
reduction.


Java does not have a memory size limit.  It's the hardware/OS.  On a
> 32-bit platform you can only address 4gb.  Then you need to account
> for the OS - kernel and process memory - which cuts that down further
> depending on the OS.  If you're stuck on 32-bit, use a 2.6 kernel to
> get the most out of your ram.  Otherwise move to 64-bit.
>
> --
> Robert Dale
> --
> TriLUG mailing list        : http://www.trilug.org/mailman/listinfo/trilug
> TriLUG Organizational FAQ  : http://trilug.org/faq/
> TriLUG Member Services FAQ : http://members.trilug.org/services_faq/
>