Java Maximum Memory on Windows Xp

Java maximum memory on Windows XP

Keep in mind that Windows has virtual memory management and the JVM only needs memory that is contiguous in its address space. So, other programs running on the system shouldn't necessarily impact your heap size. What will get in your way are DLL's that get loaded in to your address space. Unfortunately optimizations in Windows that minimize the relocation of DLL's during linking make it more likely you'll have a fragmented address space. Things that are likely to cut in to your address space aside from the usual stuff include security software, CBT software, spyware and other forms of malware. Likely causes of the variances are different security patches, C runtime versions, etc. Device drivers and other kernel bits have their own address space (the other 2GB of the 4GB 32-bit space).

You could try going through your DLL bindings in your JVM process and look at trying to rebase your DLL's in to a more compact address space. Not fun, but if you are desperate...

Alternatively, you can just switch to 64-bit Windows and a 64-bit JVM. Despite what others have suggested, while it will chew up more RAM, you will have much more contiguous virtual address space, and allocating 2GB contiguously would be trivial.

Maximum amount of memory per Java process on Windows?

There's nothing better than an empirical experiment to answer your question.
I've wrote a Java program and run it while specifying the XMX flag (also used XMS=XMX to force the JVM pre-allocate all of the memory).
To further protect against JVM optimizations, I've actively allocate X number of 10MB objects.
I run a number of test on a number of JVMs increasing the XMX value together with increasing the number of MB allocated, on a different 32bit operating systems using both Sun and IBM JVMs, here's a summary of the results:

OS:Windows XP SP2, JVM: Sun 1.6.0_02, Max heap size: 1470 MB

OS: Windows XP SP2, JVM: IBM 1.5, Max heap size: 1810 MB

OS: Windows Server 2003 SE, JVM: IBM 1.5, Max heap size: 1850 MB

OS: Linux 2.6, JVM: IBM 1.5, Max heap size: 2750 MB

Here's the detailed run attempts together with the allocation class helper source code:

WinXP SP2, SUN JVM:

C:>java -version
java version "1.6.0_02"
Java(TM) SE Runtime Environment (build 1.6.0_02-b06)
Java HotSpot(TM) Client VM (build 1.6.0_02-b06, mixed mode)
java -Xms1470m -Xmx1470m Class1 142
...
about to create object 141
object 141 created
C:>java -Xms1480m -Xmx1480m Class1 145
Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.

WinXP SP2, IBM JVM

 
C:>c:\ibm\jdk\bin\java.exe -version
java version "1.5.0"
Java(TM) 2 Runtime Environment, Standard Edition (build pwi32devifx-20070323 (if
ix 117674: SR4 + 116644 + 114941 + 116110 + 114881))
IBM J9 VM (build 2.3, J2RE 1.5.0 IBM J9 2.3 Windows XP x86-32 j9vmwi3223ifx-2007
0323 (JIT enabled)
J9VM - 20070322_12058_lHdSMR
JIT  - 20070109_1805ifx3_r8
GC   - WASIFIX_2007)
JCL  - 20070131
c:\ibm\jdk\bin\java.exe -Xms1810m -Xmx1810m Class1 178
...
about to create object 177
object 177 created
C:>c:\ibm\jdk\bin\java.exe -Xms1820m -Xmx1820m Class1 179
JVMJ9VM015W Initialization error for library j9gc23(2): Failed to instantiate he
ap.  1820M requested
Could not create the Java virtual machine.

Win2003 SE, IBM JVM

C:>"C:\IBM\java" -Xms1850m -Xmx1850m Class1
sleeping for 5 seconds.
Done.
C:>"C:\IBM\java" -Xms1880m -Xmx1880m
 Class1
JVMJ9VM015W Initialization error for library j9gc23(2): Failed to instantiate he
ap.  1880M requested
Could not create the Java virtual machine.

Linux 2.6, IBM JVM

[root@myMachine ~]# /opt/ibm/java2-i386-50/bin/java -version
java version "1.5.0"
Java(TM) 2 Runtime Environment, Standard Edition (build pxi32dev-20060511 (SR2))
IBM J9 VM (build 2.3, J2RE 1.5.0 IBM J9 2.3 Linux x86-32 j9vmxi3223-20060504 (JIT enabled)
J9VM - 20060501_06428_lHdSMR
JIT  - 20060428_1800_r8
GC   - 20060501_AA)
JCL  - 20060511a
/opt/ibm/java2-i386-50/bin/java -Xms2750m -Xmx2750m Class1 270
[root@myMachine ~]# /opt/ibm/java2-i386-50/bin/java -Xms2800m -Xmx2800m Class1 270
JVMJ9VM015W Initialization error for library j9gc23(2): Failed to instantiate heap.  2800M requested
Could not create the Java virtual machine.

Here's the code:

import java.util.StringTokenizer;

public class Class1 {

        public Class1() {}

        private class BigObject {
                byte _myArr[];
                public BigObject() {
                        _myArr = new byte[10000000];
                }
        }
    public static void main(String[] args) {
                (new Class1()).perform(Integer.parseInt(args[0]));
        }
        public void perform(int numOfObjects) {
                System.out.println("creating 10 MB arrays.");
                BigObject arr[]  = new BigObject[numOfObjects];
                for (int i=0;i <numOfObjects; i++) {
                        System.out.println("about to create object "+i);
                        arr[i] = new BigObject();
                        System.out.println("object "+i+" created");
                }
                System.out.println("sleeping for 5 seconds.");
                try {
                Thread.sleep(5000);
                }catch (Exception e) {e.printStackTrace();}
                System.out.println("Done.");
    }

}

Java Invalid Maximum Heap Size for Windows Remote Desktop

With 32-bit-windows the adress-space cannot be larger than 4GB. By default half of this is reserved for the OS, so the maximum memory available for the JVM is 2GB. Reserve some for stack and other native memory and the maximum heap-size will end up with about 1.5GB.

Using the /3G-switch for windows might increase that limit by 1GB (as it limits the OS-storage to 1GB), but that is all that is the maximum that's possible in a 32-bit OS (and with a 32-bit JVM in general).

Maximum Java heap size of a 32-bit JVM on a 64-bit OS

32-bit JVMs which expect to have a single large chunk of memory and use raw pointers cannot use more than 4 Gb (since that is the 32 bit limit which also applies to pointers). This includes Sun and - I'm pretty sure - also IBM implementations. I do not know if e.g. JRockit or others have a large memory option with their 32-bit implementations.

If you expect to be hitting this limit you should strongly consider starting a parallel track validating a 64-bit JVM for your production environment so you have that ready for when the 32-bit environment breaks down. Otherwise you will have to do that work under pressure, which is never nice.

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Edit 2014-05-15: Oracle FAQ:

The maximum theoretical heap limit for the 32-bit JVM is 4G. Due to various additional constraints such as available swap, kernel address space usage, memory fragmentation, and VM overhead, in practice the limit can be much lower. On most modern 32-bit Windows systems the maximum heap size will range from 1.4G to 1.6G. On 32-bit Solaris kernels the address space is limited to 2G. On 64-bit operating systems running the 32-bit VM, the max heap size can be higher, approaching 4G on many Solaris systems.

(http://www.oracle.com/technetwork/java/hotspotfaq-138619.html#gc_heap_32bit)

Maximum memory usage in a 32 bit guest system

I think the problem is that the JVM needs a continous adress space which, although in theory ~3GB of memory are available, I can not get because some libraries are loaded in random locations. The only fast solution seems to be switching to a non-Windows system. Thank you Danielson.

See also the answer by Uri on Java maximum memory on Windows XP

java 1.6 32-bit min and max heap memory issue

In your case, the limit is most likely the 32 bit architecture and the way that Windows is apportioning the virtual address space.

According to the Oracle JVM FAQ, you can only expect to get 1.4Gb to 1.6Gb on a 32bit JVM on Windows.

What is max heap size I can allocate for JVM on Win32 machine?

Got the answer in this SO link

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