Sunday, August 2, 2009

Maximum heap size limit of java is smaller than you think

You might think that on a 32-bit OS, a process should be able to address address 2^32 = 4Gb of address space, however in practice some of the address space is used by the OS kernel and so is not available to the process. So there are limitations to how much a process can address and it can vary depending on the platform and the versions of JDK. There are programs like IBM Heap Analyzer requires large amount of memory while analyzing heap dumps taken from JVM with setting of max heap size of -Xmx 1400M(1.4GB) or more and while analyzing, your jvm might very well run out of memory, hence you might needed a 64-bit OS running 64-bit JVM to even analyze a heap dump taken in a 32-bit JVM. Here below is the table lists the max heap size a JVM can take in the respective platform and the different versions.

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JVM Version



Xmx Max Heap Size

Error When JVM not able to allocate memory


Java(TM) SE Runtime Environment (build 1.6.0-b105) / Java HotSpot(TM) Client VM (build 1.6.0-b105, mixed mode, sharing)

Windows XP

32 bit


Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.


Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2)
Classic VM (build 1.4.2, J2RE 1.4.2 IBM Windows 32 build cn1420-20040626 (JIT enabled: jitc))

Windows XP

32 bit


[ Unable to allocate an initial java heap of 1724907520 bytes. ]
[ **Out of memory, aborting** ]
[ ]
[ *** panic: JVMST016: Cannot allocate memory for initial java heap ]

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.


Java(TM) SE Runtime Environment (build pwi3260sr2-20080818_01(SR2))
IBM J9 VM (build 2.4, J2RE 1.6.0 IBM J9 2.4 Windows XP x86-32 jvmwi3260-20080816_22093 (JIT enabled, AOT enabled)

Windows XP

32 bit


JVMJ9VM015W Initialization error for library j9gc24(2): Failed to instantiate heap; 1814M requested
Could not create the Java virtual machine.


java version "1.6.0_13"Java(TM) SE Runtime Environment (build 1.6.0_13-b03)Java HotSpot(TM) Server VM (build 11.3-b02, mixed mode)


32 bit


Error occurred during initialization of VMCould not reserve enough space for object heapCould not create the Java virtual machine.

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