I have a Java project that needs a lot of memory to run. When I change the flags here:
It works fine, however I still need a bigger Heap size but whenever I choose a bigger size like 2g or something like that it always shows the following message:
Am I doing something wrong? And what can I do to correct this issue, I looked everywhere but can't seem to find a solution and I really need this for an assignment that is to be due sooner than I hoped...
EDIT: I should add that my computer has 8GB ram so that shouldn't be the issue and I'm working on Windows 10 if that matters.
EDIT1: When I click on help->about I get this window:
How can I conclude from here if my jvm is 32 or 64 bit?
How can I conclude from here if my jvm is 32 or 64 bit?
You are using a 32bit JVM.
A 64bit JVM includes that information in the version string, e.g.:
1.8.0_92; Java HotSpot(TM) 64-Bit Server VM 25.92-b14
A 32bit process is restricted to 2GB of memory and with Java you usually can't usually use more then about 1.2GB. I think this depends on the Windows version and configuration.
So just remove the 32bit JDK and install the 64bit one, then you can use all the 8GB that your computer has.
I have one really weird problem.
I have one Swing Application which we recently upgraded, that does not run at all in a Java 1.7/1.8 64bit enviroment.
More specifically, the application works perfectly in 32bit Java installations of 1.7.0_52+, but if you place it in a 64bit enviroment it does not open at all.
Running it from the console with the -verbose, the last message before it stops loading is:
[Loaded sun.awt.AWTAutoShutDown$1 from c:\Program Files\Java\jre1.8.0_65\lib\rt.jar]
There is no message in any log above that suggests an error has occured, and no exception or other message thrown. The application's java enviroment remains in memory with a cpu usage of ~40%.
What makes this wierd is that the same application runs from the same PC if I launch it via eclipse. There is only one java installation on my PC, and both the application and Eclipse use this same JDK.
I am unable to think of anything that could cause a problem, and I am at a loss. Does anyone have anyidea?
The 64-bit JVM using 32-bit references can address 32+3 bits of address space as it can assume the lowest 3 bits of an objects address is 0.
Most 32-bit JVMs are limited to around 1.2-1.5 GB.
I want to download Bea JRockIt 5 because the JRE doesn’t seem to be able to allocate VM more than 1.6 GB.
please i not find the link for download the JRockIT jre
I use machine 32 bits windows7 and ram 3GB.
Thanks in advance
The bottom line is that the limit you are seeing is not actually a JVM imposed limit. So changing to JRockit is not going to help.
Most 32-bit Windows operating systems limit the virtual memory for a user application (such as a JVM) to 2Gb. However, there is a boot switch for Windows Server 2003 that enables applications up to 3Gb ... on hardware that supports PAE : http://msdn.microsoft.com/en-us/windows/hardware/gg487508.aspx.
Your alternatives are:
If you are running Windows Server 2003 - do what the link says.
Switch to 32 bit Linux or 32 bit Solaris. Both allow more than 2Gb for user applications.
Switch to a 64 bit operating system.
I don't know why a simple Google search didn't suffice, but this is clearly available on OTN.
As far as allocation of memory for the JVM is concerned, it is unlikely that you will be able to get any amount more than 2GB. See this related question and the most voted answer.
i tried to compare my java web app behaviour on 32 bit windows and 64 bit linux.
When i view the memory usage via jconsole i find very different graph of memory usage.
On windows the appl never touches 512m.
However when i run on linux 64bit with 64 bit VM the memory keeps invcreasing gradually and reaches peak value about1000m very quickly and i also get oome error related to GC over head limit exceeded. on linux whenever i do manual run GC it drops below to less than 100m.
Its like the GC does seem to run so well as it does on windows.
On windows the app runs better with even more load.
How do i find the reason behind this?
Iam using jdk1.6.0.13
min heap:512m and max heap 1024m
EDIT:
Are you using the same JVM versions on both Windows and Linux?
yes.1.6.0.13.
Are you using the same garbage collectors on both systems?
I noticed in jconsole and i see that the gc are different.
Are you using the same web containers on both systems?
yes.Tomcat.
Does your webapp rely on native libraries?
Not sure. I use tomcat+spring+hibernate+jsf.
Are there other differences in the configuration of your webapp on the two platforms?
No
What exactly was the error message associated with the OOME?
java.lang.OutOfMemoryError: GC overhead limit exceeded
How long does it take for your webapp to start misbehaving / reporting errors on Linux?
The difference in usage pattern is seen after i leave it running for say 3hrs. The error appears after like a day or 2 days since by then avg memory usage is seen around 900 mb mark.
A 64bit JVM will naturally use a lot more memory than a 32bit JVM, that's to be expected (the internal pointers are twice the size, after all). You can't keep the same heap settings when moving from 32bit to 64bit and expect the same behaviour.
If your app runs happily in 512m on a 32bit JVM, there are no reasons whatsoever to use a 64bit JVM. The only rationale for doing that is to take advantage of giant heap sizes.
Remeber, it's perfectly valid to run a 32bit JVM on a 64bit operating system. The two are not related.
There are too many unknowns to be able to explain this:
Are you using the same JVM versions on both Windows and Linux?
Are you using the same garbage collectors on both systems?
Are you using the same web containers on both systems?
Does your webapp rely on native libraries?
Are there other differences in the configuration of your webapp on the two platforms?
What exactly was the error message associated with the OOME?
How long does it take for your webapp to start misbehaving / reporting errors on Linux?
Also, I agree with #skaffman ... don't use a 64bit JVM unless your application really requires it.
I noticed Sun is providing a 64-bit version of Java. Does it perform better than the 32-bit version?
Almost always 64 bits will be slower.
To quote Sun from the HotSpot FAQ:
The performance difference comparing
an application running on a 64-bit
platform versus a 32-bit platform on
SPARC is on the order of 10-20%
degradation when you move to a 64-bit
VM. On AMD64 and EM64T platforms this
difference ranges from 0-15% depending
on the amount of pointer accessing
your application performs.
There are more details at the link.
Define your workload and what "perform" means to you.
This is sort of a running annoyance to me, as a performance geek of long standing. Whether or not a particular change "performs better" or not is dependent, first and foremost, on the workload, ie, what you're asking the program to do.
64 bit Java will often perform better on things with heavy computation loads. Java programs, classically, have heavy I/O loads and heavy network loads; 64 bit vs 32 bit may not matter, but operating systems usually do.
64-bit perform better if you need much more than 1.2 GB. On some platforms you can get up to 3 GB but if you want 4 - 384 GB for example, 64-bit is your only option.
I believe Azul supports a 384 GB JVM, does anyone know if you can go higher?
I know that this question is quite old and the voted answers were probably correct at the time when they were written. But living in 2018 now, things have changed.
I just had an issue with a Java client application running on Win 10 64Bit on a Java 8 32Bit JVM. It was reading 174 MB of data from an HttpsURLConnection's InputStream in 26s which is awfully slow. The server and network were proven not to be the cause of this.
Thinking "Hey, there cannot be a huge difference between 32Bit and 64Bit JRE" it took some time until I tried having the very same code executed by a 64Bit JVM. Fortunately, in the end I did it: It was reading the very same 174MB in 5s!
I don't know if I could make it even faster, but the key take-away is this:
jre1.8.0_172 32Bit : 6.692MB/s
jre1.8.0_172 64Bit : 34.8MB/s
for the very same jar file being executed on Windows 10 64Bit.
I have no idea what could be the reason for this, but I can answer this question by "Yes, 64Bit Java is better than 32Bit Java". See also the numbers in the answer of my question regarding this issue.
On most CPU architecures 32-bits is faster than 64-bit, all else being equal. 64-bit pointers require twice as much bandwidth to transfer as 32-bits. However, the x64 instruction set architecture adds a bit of sanity over x86, so it ends up being faster. The amount of handling of long types is usually small.
Of course it also depends upon the implementation of Java. As well as the compiler, you might find differences in the implementation; for instance, NIO assumes 64-bit pointers. Also note that Sun previously only shipped the faster server HotSpot implementation for x64. This meant that if you specified -d64, you would also switch from client to server HotSpot, IIRC.
Some improvements: operations with doubles on 64 bits compute equally fast as floats on 32 bits, as well as operations on long at 64 bit compared to int.
So if you are running code with tons of longs you might see a real improvement.
My experience differs from the other answers.
Java 64bit may be faster than 32bit. At least with my tests it always was! The pointer argument is not valid when less than 4GB are used because then the 64bit-VM will also use short pointers internally. You get however the faster instruction set of the 64bit CPUs!
I tested this with Windows 7 and JDE1.8.0_144, but maybe the real reason are different internal JVM setting. When you use the 64-bit JVM it starts in "server" mode, while the 32-bit VM starts in "client" mode.
Yes, especially if your code is built to target a 64 bit platform.