How to set up a really big JVM heap size

jvm

According to the JVM 6 documentation, server class machines receive by default an initial heap size as 1/4 RAM or 1GB. Considering our Solaris 64Bit server has 64 GB, the initial heap size will default in as 256MB. Therefore, I need to set manually the heap size using the XMX parameter for 4GB. Though, when I add "-Xmx4096M", Tomcat does not start. Here is the error message:

Invalid maximum heap size: -Xmx4096M
The specified size exceeds the maximum representable size.
Could not create the Java virtual machine.

What should be my command line parameters to allow my heap to grow up to 4GB?

Best Answer

Thanks for all your input, guys! Though, the output of my java -version mentions mixed mode which means that it is 64 bits. The real solution is adding -d64 to force it to run in 64 bits and therefore allocate the 4GBs.

Related Solutions

Java – the default maximum heap size for Sun’s JVM from Java SE 6

java 1.6.0_21 or later, or so...

$ java -XX:+PrintFlagsFinal -version 2>&1 | grep MaxHeapSize
uintx MaxHeapSize                         := 12660904960      {product}

It looks like the min(1G) has been removed.

Or on Windows using findstr

C:\>java -XX:+PrintFlagsFinal -version 2>&1 | findstr MaxHeapSize

Java – Can the JVM max heap size be dynamic

But, is there a way to make that value dynamic?

Literally, no. The max heap size is set at JVM launch time and cannot be increased.

In practice, you could just set the max heap size to as large as your platform will allow, and let the JVM grow the heap as it needs. There is an obvious risk in doing this; i.e. that your application will use all of the memory and cause the user's machine to grind to a halt. But that risk is implicit in your question.

EDIT

It is worth noting that there are various -XX... GC tuning options that allow you to tweak the way that the JVM expands the heap (up to the maximum).

Another possibility is to split your application into 2 parts. The first part of the application does all of the preparation necessary to determine the "size" of the problem. Then it works out an appropriate max heap size, and launches the memory hungry second part of the application in a new JVM.

This only works if the application can sensibly be partitioned as above.
This only works if it is possible to compute the problem size. In some cases, computing the problem size is tantamount to computing the result.
It is not clear that you will get better overall performance than if you just let the heap grow up to a maximum size.

Best Answer

Related Solutions

Java – the default maximum heap size for Sun’s JVM from Java SE 6

Java – Can the JVM max heap size be dynamic

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