Maximum heap size for 32 bit or 64
bit JVM looks easy to determine by looking at addressable memory space like 2^32
(4GB) for 32 bit JVM and 2^64 for 64 bit JVM. The confusion starts here because you can not really set 4GB as the maximum heap size for 32 bit
JVM using -Xmx JVM heap options. You will get could not create the Java virtual machine
Invalid maximum heap size: -Xmx
error. There could be much different reasons why maximum heap space for
JVM is less than its theoretical limit and varies from one operating system to
other e.g. different in Windows, Linux, and Solaris.
I have seen a couple of comments on my post 10 points on Java Heap Space regarding what is maximum heap space for Java or 32 bit JVM or 64 bit JVM and why Windows allows only up to 1.6G memory as maximum heap space etc.
In this Java article, I have collected some of the frequently asked questions around maximum heap space on both 32 and 64 bit JVM and tried to explain them.
I have seen a couple of comments on my post 10 points on Java Heap Space regarding what is maximum heap space for Java or 32 bit JVM or 64 bit JVM and why Windows allows only up to 1.6G memory as maximum heap space etc.
In this Java article, I have collected some of the frequently asked questions around maximum heap space on both 32 and 64 bit JVM and tried to explain them.
FAQ Maximum Java Heap Space on 32 and 64 bit JVM
Here is a list of some confusions I have seen on Java programmers regarding
maximum heap space of 32 and 64 bit Java Virtual Machines :- What is the maximum heap size for 32 bit JVM? 2GB or 4GB?
- Why my JVM not able to start on windows when maximum heap space around 1600M?
- Why Linux or Solaris allow more maximum heap size than windows for same, 32 bit JVM?
- Can we set more than 4GB as maximum heap size for 32 bit JVM running on 64 bit or x64 operating system?
- What is maximum heap size for 64 bit or x64 JVM, Is it 8GB or 16GB?
- Can I specify more than 1GB as heap space if physical memory is less than 1GB?
If you also have similar confusion on JVM maximum heap space no
matter whether it's for your own Java application or any Java web or application server like Tomcat, JBoss or WebLogic, This discussion applies to all of them.
What is
maximum heap size for 32 bit JVM? 2GB or
4GB?
This confusion comes because of a sign bit, many programmers think in terms
of signed integer and they think maximum addressable memory (size of address
bus) for 32-bit architecture is 2^32-1 or 2GB
and this confusion is supported by fact that you can not provide maximum
heap space as 2GB on a windows machine. But this is wrong. Memory is nothing to
do with a signed or unsigned bit as there is no negative memory address. So the theoretical limit for maximum heap size on 32 bit JVM is 4GB and for 64 bit JVM
it's 2^64.
Why JVM
not able to start on Windows XP when maximum heap space around 1600M?
This problem is most obvious on Windows platforms like Windows XP, which
tries to allocate a contiguous chunk of memory as requested by -Xmx JVM parameters. Windows
reserves some space for his own and seems also allocate memory around half of memory address bar, which consequently reduces contiguous memory space
somewhere less than 2GB, around 1500 to 1600M and when you give more than this
size, JVM throws an error as.
Could not create the Java virtual machine.
Invalid initial heap size: -Xms1.5G
Remember, this limit on heap space is due to the Windows operating system's
own behavior. You can set maximum heap space, more than this size in Linux or
Solaris. Though maximum heap size for 32 bit or 64 bit JVM will always be less
than the theoretical limit of addressable memory. By the way, you can get this error
due to many reasons, see How to fix Invalid Initial and Maximum heap size in JVM for more details.
Why Linux
or Solaris allow more maximum heap size than windows for same, 32 bit JVM?
This point is also related to the second. Though there could be multiple reasons for that I think It could be
because of Windows trying to allocate a contiguous chunk of memory as Java heap
space. Happy to hear your opinion on this.
Can we
set more than 4GB as maximum heap size for 32 bit JVM running on 64 bit or x64
operating system?
This is a tricky question as you are
running 32 bit JVM on the x64 server. In my opinion, you can set up to 4GB for 32 bit
JVM but not more than that. Though x64 Servers has more memory for his needs
and since every process can have up to 2^64 bit it may
look perfectly OK for 32 bit JVM to accept 4GB
as maximum heap size. In practice, I have tried both Linux and Solaris
servers setting the maximum heap size as 4G but it didn’t accept. Solaris goes closer to 4GB by allowing up to 3.6G (approx).
What is
maximum heap size for 64 bit or x64 JVM, Is it 8GB or 16GB?
This question mostly arises because of available physical memory on the machine. As no system currently have 2^64 bit of
physical memory or RAM and often high-end servers have memory around 8G, 16GB or
32GB. Theoretical maximum memory for x64 machines is 2^64 bit but again it depends on how much your operating systems allow. I read somewhere
that Windows allowed a maximum of 32GB for 64 bit JVM.
Can I
specify more than 1GB as heap space if physical memory is less than 1GB?
Theoretically yes, because the operating systems can use virtual memory and
swap pages between physical memory and virtual memory when there is no room in
physical memory. Practically, if you are running on windows then it depends on how
far you can go, I have run Java program with -Xmx1124M even though
my machine has less than 1GB RAM.
That’s all on what is maximum Java heap space for 32 bit and 64 bit
JVM. As you see maximum heap size depends upon the host operating system. Solaris and Linux provide more heap space than windows and that could be one
of the many reasons that Java Server application mostly runs on UNIX based
systems. Let me know what’s your thought and experience on maximum Java heap space for x86 and x64 JVM running on both x86 and x64
machines.
Other Java JVM Tutorials from Javarevisited Blog
11 comments :
A very important point about why you cannot allocate 4GB an only allocate a lot less than 4GB to a java process on a 32-bit machine. The threads created by your java process have their own stackspace and that also has to fit into this 4GB limit (normally due to OS overhead this limit is 3.2GB and not 4GB). Now this default thread-stackspace (Xss) is different on different operating systems and hence the difference between total memory youcan allocate to heap.
As I mentioned above,
Max Heap = 3.2GB - total thread-stackspace.
One quick way to use more heap on a multi-threaded java app is to reduce your Xss.
You can refer my blog for exact numbers.
http://oakgreen.blogspot.sg/2011/08/thread-count-supported-by-jvm-on.html
How much heap size can be allocated if the physical memory/RAM is 3 GB? I got this question in written test. Can somebody say how much and why ?
What is the maximum memory limit for a 64 bit JVM? Also I heard that Java Garbage Collectors are not optimized for large heap sizes? Considering that in mind, How much maximum heap size should be without compromising performance?
Can any one please provide following details to me, I need this to submit to my project manager
Default Heap Size for 32 bit JVM in 32-bit Windows
Maximum Heap Size for 32 bit JVM in 32-bit Windows
Default Heap Size for 32 bit JVM in 32-bit Redhat Linux
Maximum HHeap Size for 32 bit JVM in 32-bit Redhat Linux
Default Heap Size of 32 bit JVM in 32-bit Solaris x86
Maximum Heap Size of 32 bit JVM in 32-bit Solaris x86
Default Heap space for 64 bit JVM in 64 bit Windows 2003 Server
Maximum Heap space for 64 bit JVM in 64-bit Windows 2003 Server
Default Heap space for 64 bit JVM in 64 bit Linux
Maximum Heap space for 64 bit JVM in 64-bit Linux
Default Heap space for 64 bit JVM in 64 bit Solaris x86
Maximum Heap space for 64 bit JVM in 64-bit Solaris x86
Thank you
How to reduce java heap space (out of memory) exception... Java heap space is already set to max.. do the unhandled java runtime exception will consume the memory in java heap?
If you want to get rid of OutOfMemoryException, one immediate thing you can do is to switch to a 64-bit JVM, that will allow you to allocate more memory than your 32-bit JVM and can handle capacity better. Ofcourse, this is only work if you don't have a memory leak, otherwise no mater how much memory you allocate, you will eventually run out with it after some time.
worth remembering that most 64-bit JVMS run with 32-bit references for heaps up to 32 GiB. In Java 8 up to 64 GiB.
I have doubt from the question 2 you have mentioned that Java runs out of memory if xmx is 1600mb in windows. But in question 5 you have mentioned that OS will use swap memory in harddisk if it crosses the heap memory size.
2^32 -1 is 4GB, not 2GB. I think that you meant a 32-bit signed int max would be 2^31-1
I have a big doubt am using java 32 bit on a 64 bit operating server.While i trying to extends jvm memory in tomcat multiple instance(tomcat 7),startup.bat is not starting .Can anyone help me out with this issue?
And also what is the maximum heap size that we can give for apache tomcat 7 where as am using 64 bit operating sever 32 GB RAM,32 bit JVM
Post a Comment