I am running java process through main class on java 8. I have not specified anywhere min(Xms) and max(Xmx) heap size. But when i check through visualVM it's
4267704320(i.e. 4.26 GB) which is the default max heap size for a given process(confirmed through windows command also which is
-XX:+PrintFlagsFinal -version 2>&1 | findstr MaxHeapSize. similarly on linux box too).
My question is if my process(on linux machine) requires more 5 GB(i have 30 GB RAM), will my process be allocated 5 GB memory when i have not specified
any explicit heap size(Xms and Xmx) parameters.
Given your the available RAM on your machine, if you are running a 64-bit JVM in server mode, then yes, the heap size will be able to go up to approximately 7.5 GB.
Documentation (I highlighted the relevant parts):
Client JVM Default Initial and Maximum Heap Sizes
The default maximum heap size is half of the physical memory up to a physical memory size of 192 megabytes (MB) and otherwise one fourth of the physical memory up to a physical memory size of 1 gigabyte (GB).
Server JVM Default Initial and Maximum Heap Sizes
The default initial and maximum heap sizes work similarly on the server JVM as it does on the client JVM, except that the default values can go higher. On 32-bit JVMs, the default maximum heap size can be up to 1 GB if there is 4 GB or more of physical memory. On 64-bit JVMs, the default maximum heap size can be up to 32 GB if there is 128 GB or more of physical memory. You can always set a higher or lower initial and maximum heap by specifying those values directly; see the next section.
Again, assuming a 64-bit JVM running in server mode, the default max heap size according to the documentation will be one fourth of your total RAM. So approximately 7.5 GB in your case (1/4 of 30 GB).
If running a 32-bit JVM in server mode, you'll be capped at 1 GB. And in client mode, your max will be 256 MB.
Related
I am running a Java application on a windows server (32-bit, 12GB RAM) with the
-Xmx8g and I am getting an error saying
Invalid Maximum Heap Size.
The specified size exceeds the maximum representable size.
But the same application is running on my local machine (64-bit, win-7, 6GB RAM) with the same -Xmx8g command.
I dont have the option of changing the OS of the server. Is there any possible solution to this?
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).
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.
Heap is part of RAM.But still there is a limit that we can not define heap size beyond some percentage of RAM.For example:- i have 32 bit winodws xp OS and 4
GB RAM. But i can not declare the heap size more than 1600 MB. My question here why we can not declare heap size to some large value say 3GB which
is lower than my 4GB RAM(as in 32 Bit can ustilize up to 4gb of RAM)? This is true for single process.
I mean i can start two tomcat or any other java process
allocating 1600MB heap size to each but i can not allocate 3200MB to single process.what is the reason that behind that?
32-bit windows only allows 2GB of address space to a single process (without special extensions enabled.) The OS keeps the other 2GB for itself. Then on top of that Heap is not all of the memory that JVM needs. There is permgen space, and the memory that the code of the JVM itself uses.
If its not 64 bit 4GB cannot be allocated.
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.