Re: 32G ram

From:

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 18 Dec 2012 20:22:02 -0500

Message-ID:

<50d116bd$0$281$14726298@news.sunsite.dk>

On 12/18/2012 4:19 AM, Nigel Wade wrote:

On 17/12/12 08:39, Donkey Hottie wrote:

17.12.2012 05:09, Arne Vajh?j kirjoitti:

On 12/16/2012 10:05 PM, mcheung63@gmail.com wrote:

i got 32GB ram, why i can't -Xmx2G, it got an error "Could not
create the Java Virtual Machine"

/root>free -m
total used free shared buffers
cached
Mem: 32387 16973 15413 0 243
11906
-/+ buffers/cache: 4823 27563
Swap: 1906 0 1906
/root>uname -a
Linux localhost.localdomain 3.6.9-2.fc17.i686.PAE #1 SMP Tue Dec 4
14:15:28 UTC 2012 i686 i686 i386 GNU/Linux

32 bit or 64 bit Java?

Apparently 32 bit, as the i686 OS is 32 bit PAE too.

32bit Java on 32bit Linux should allow an application of up to 4GB. How
much can of that can be allocated to the heap depends on the particular
application. I've allocated more than 2G to heap on a 32bit Linux
system, see this old thread on Google Groups:
https://groups.google.com/forum/?hl=en-GB&fromgroups=#!topic/comp.lang.java.programmer/iGr3bxL9ZCA

32 bit Java can in theory use up to 3 GB on 32 bit OS on x86 if the
border between process and system is changed (/3GB). But on Windows
JRocket is supposedly the only Java that can do it.

32 bit Java can never use 4 GB on 32 bit OS on x86, because that
does not leave any address space for the OS.

32 bit Java can use 4 GB on 64 bit OS on x86, because the OS
are running in 64 bit addresses (or something like that), if various
requirements are in place. I don't know what Java versions support
that.

Arne