I am using a 64 bit Windows 10 system with 32Gb of RAM. One of my 32 bit java application requires a lot of memory so I decided to change the minimum heap size to -Xms4096m at the runtime parameter field in the java configuration dialogue.
However, I soon realised that it would not do anything because apparently my system's maximum heap size is only 247.50mb (which is way too small for a 64 bit system). I am using a 32 bit java so I am expecting a max heap size of around 4GB. Can anyone tell me what determines the maximum heap size and how do I change it?
UPDATED: I understand that the maximum I can allocate is 2GB for a 32 bit system. So my question now is how come for my system, its only 247.50mb?
BELOW ARE MY Java Settings:
Related
I have a RHEL 6 32 bit system installed in a 64 bit hardware. The kernel version is,
2.6.32-431.17.1.el6.i686
I posted a very detailed question and answer here. Now, I have the JVM which is also 32 bit. I believe even if I install a 64 bit JVM, I will be allowed to use only upto 3 GB since I have only 32 bit OS.
So, my question is, a single process can have more than 4 GB memory and still be used in a 32 bit system. In a similar manner, if I set my maximum heap size to 2 GB in the 32 bit OS, will I still be able to use the memory?
For instance, if my java application requires 10 GB memory, and I set the maximum heap size to 2 GB, my question is, once the 2 GB is exhausted, will my application terminate or swap the address space and continue working?
I am also interested in knowing a good limit on the maximum heap memory limit.
> I believe even if I install a 64 bit JVM,
No, you can't do this. You can only run 32 bit applications on a 32 bit linux OS - even if the underlying hardware is 64 bits.
> a single process can have more than 4 GB memory and still be used in a 32 bit system.
No, a 32 bit linux installation only supports 32 bit applications, and that means you're limited to an address space of max 4GB. For linux, the kernel needs 1 GB of that space. Native libraries, stack space and other things also needs a piece of the address space, leaving you with memory available for the heap of around 2-2.5GB.
The PAE feature enables the OS to utilize more than 4GB of memory in total, but individual processes are still limited to 4 GB of address space.
> if my java application requires 10 GB memory, and I set the maximum heap size to 2 GB, my question is, once the 2 GB is exhausted, will my application terminate
Yes, if the application needs more memory, it will terminate with an OutOfMemoryError
> I am also interested in knowing a good limit on the maximum heap memory limit.
There is no universal answer - it depends on the application and whatever else you want to run on your system.
I believe even if I install a 64 bit JVM, I will be allowed to use only upto 3 GB since I have only 32 bit OS.
You can install it, but it won't run. Only a 64-bit OS can run a 64-bit application, whether it is a JVM or any other program.
So, my question is, a single process can have more than 4 GB memory and still be used in a 32 bit system.
Not directly. A 32-bit program can only use about 1.5 to 3 GB direct depending on the OS. A program can use a disk cache which is much larger. It can also use other program which themselves use more memory (in total)
In a similar manner, if I set my maximum heap size to 2 GB in the 32 bit OS, will I still be able to use the memory?
If you have a 2 GB heap this should be fine so long as the process doesn't exceed how much memory your whole process can use. The heap is not all the memory used of course.
if my java application requires 10 GB memory, and I set the maximum heap size to 2 GB, my question is, once the 2 GB is exhausted, will my application terminate or swap the address space and continue working?
If you need more than 10 GB, you should ensure you have at least 12 GB of main memory AND a 64-bit OS. What will happen if you don't have enough will range from the program running very slow, or your program crashing, or in extreme cases your whole machine will practically stop.
Java applications run very badly once they start swapping. They either crawl to a stop, or they can practically stop the machine.
I am also interested in knowing a good limit on the maximum heap memory limit.
A good limit is less than your main memory size. The default limit for the server JVM is 1/4 of main memory. Without more information, I would leave it as it is.
I am using 32 bit version of Java in windows 7 64 bits. The system has a RAM of 6 GB. But when JVM is allocated memory by OS, it doesnot goes beyond 1.5 GB (same as in 32 bit OS). What are the possible reasons, that JVM is not allowed sufficient memory. And if possible how to fix it? I cannot upgrade to 64 bit JVM.
A 32-bit process on Windows is still subject to the same limits as running on a 32-bit Windows OS. See the answers to this question.
How much memory can a 32 bit process access on a 64 bit operating system?
This guidance from Oracle suggests that a 32-bit JVM can use approximately 1.5GB.
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.
As indicated by this article:
The default maximum heap space is 1/2 of physical memory of size upto 192 bytes and 1/4th of physical memory for size up to 1G.
I know you have more than 1G, but maybe this also applies for you
32 bit application will not be able to use more that 4GB of RAM. In practice, it will not be able to use more than 3GB because it needs some virtual memory space reserved for operating system.
Besides that, by default JVM allocates up to a quarter of available RAM. If you want to override this use option:
java -XX:DefaultMaxRAMFraction=1
It should use all available RAM that is feasible for 32 bit application.
Source: http://jvm-options.tech.xebia.fr/#
To be able to use more memory you have to upgrade to 64 bits. Unfortunately a 64 bit JVM cannot load 32 bit dlls, so the calls to the dll must be made from a different process, and you have to use an rpc mechanism to talk with the process instead of using the dll directly. It's a lot. of work but it can be done.
My Jenkins build is running out of memory because of JUnits. When I try to give it (the JUnits) more than 4GB it errors out. I am using Linux as my build machine.
Invalid maximum heap size: -Xmx4096m
I am just wondering, is there a upper limit to how much heap size JUnits can use?
"For a 32-bit process model, the maximum virtual address size of the process is typically 4 GB, though some operating systems limit this to 2 GB or 3 GB. The maximum heap size is typically -Xmx3800m (1600m) for 2 GB limits), though the actual limitation is application dependent. For 64-bit process models, the maximum is essentially unlimited."
Found a pretty good answer here:
Java maximum memory on Windows XP
Memory is allocated to JVM not JUnit or any other class.
and there is limit on 32-bit system to assign max of 4Gb but if you requires more memory then move to 64 bit machine as there is no limit of max memory allocation .
i would guess you are using a 32 bit jvm ..
check this post:
Maximum Java heap size of a 32-bit JVM on a 64-bit OS
It's not JUnit but JVM. 4GB heap is too much for 32-bit JVMs.
I know the default Java heap memory is 128 MB. Since it is the default, I want to know whether this memory get automatically changed according to the RAM size. For an example, for a machine with 128 MB RAM, heap memory 128 is too much and it should be automatically changed. Because if an application use all of 128 heap, PC will end up in a trouble.
please help.
In Java 1.6 update 18 (and later), if unspecified, the default heap-size in a client JVM follows these rules:
The default maximum heap size is half of the physical memory up to a
physical memory size of 192 megabytes and otherwise one fourth of the
physical memory up to a physical memory size of 1 gigabyte.
For
example, if your machine has 128 megabytes of physical memory, then
the maximum heap size is 64 megabytes, and greater than or equal to 1
gigabyte of physical memory results in a maximum heap size of 256
megabytes.
Taken from the 1.6.0_18 update notes
In previous releases of Java heap size was NOT variable by default.
No, it won't be automatically changed unless you ask for it on startup using the -Xmx option.
You can't get more than 2 GB on a 32 bit machine in any case. If you need more than that, you'll have to get a 64 bit operating system with lots of RAM.
You can specify JVM heap size by using aptions -Xmx and -Xms
-Xmx - Max Size.
-Xms - Min Size.
You specify like
-Xmx64m -Xms32m (for 64 and 32 MB)
No. It is not automatically changed. Look here for more on HotSpot JVM memory options .
More Here on handling Java OutOfMemoryError.
I run a Java code with the following command:
$ java -Xms4G -Xmx4G myjavacode
My cpu's RAM capacity is 6GB.
However it always fail to execute giving me this
error message:
Invalid initial heap size: -Xms5G
The specified size exceeds the maximum representable size.
Could not create the Java virtual machine
Is there any way to set up Java option so that we can
execute the code?
You've exceeded the maximum heap size of your JVM. This is both JVM and OS dependent. In most 32-bit systems the maximum value will be 2Gb, regardless of the physical memory available.
By default Java will run in 32 bit mode. Be sure to give it the -d64 option to put it into 64 bit mode. Once in 64-bit mode, you shouldn't have any trouble allocating a 6GB JVM.
Actually, the maximum memory size on 32-bit systems can vary, being anything up to 4 GB, but 2 GB is a common value. It's often possible to re-link your kernel to increase this to 3 or 3.5 GB. The issue, of course, is that you just don't have the address space to map more memory. Have you tried a 64-bit machine?
Also, remember to set your ulimit higher before you do this.