--Xmx 的 Java JVM 限制

Question

I am running a java app on a Windows 10 machine via

JAVA -Xms1500M -Xmx1600M -jar appname.jar

The app fails after a while with an error stating not enough heap space. When it is running using Task Manager I can see I am using about 50% of the total memory available on the machine.

If I try and increase the -Xmx space then I get an error saying it cannot be allocated - why is this as there is plenty of memory free?

The Java app is a 3rd party and I know it runs on colleagues pcs

My JVM version is

Answer 1

I suspect that you are running a 32 bit JVM. (According to the version info you have an Oracle release, and Java 8 was the last versin that Oracle provided 32 bit downloadables for.)

Assuming that is the case, the max heap size for a 32 bit Java on Windows is limited to between 1.4 and 1.6GB. The limit is a result of the way that Windows allocates virtual address spaces. For more details read:

• Frequently Asked Questions About the Java HotSpot VM: "Why can't I get a larger heap with the 32-bit JVM?"

The solution is to download and install a 64 bit Java release for Windows. You want a download for the "x86-64" architecture.

(I notice that you are running 1.8.0_101. That was released in July 2016 and is way out of date. At time of writing, the most recent Java 8 release is 1.8.0_231.)

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The Java app is a 3rd party and I know it runs on colleagues pcs

They probably have installed 64 bit Java.