Increase heap size in Java

I am working on a Windows 2003 server (64-bit) with 8 GB RAM. How can I increase the heap memory maximum? I am using the -Xmx1500m flag to increase the heap size to 1500 Mb. Can I increase the heap memory to 75% of physical memory (6 GB Heap)?

Solution 1:

You can increase to 2GB on a 32 bit system. If you're on a 64 bit system you can go higher. No need to worry if you've chosen incorrectly, if you ask for 5g on a 32 bit system java will complain about an invalid value and quit.

As others have posted, use the cmd-line flags - e.g.

java -Xmx6g myprogram

You can get a full list (or a nearly full list, anyway) by typing java -X.

Solution 2:

It is possible to increase heap size allocated by the JVM by using command line options Here we have 3 options

-Xms<size>        set initial Java heap size
-Xmx<size>        set maximum Java heap size
-Xss<size>        set java thread stack size

java -Xms16m -Xmx64m ClassName

In the above line we can set minimum heap to 16mb and maximum heap 64mb

Solution 3:

On a 32-bit JVM, the largest heap size you can theoretically set is 4gb. To use a larger heap size, you need to use a 64-bit JVM. Try the following:

java -Xmx6144M -d64

The -d64 flag is important as this tells the JVM to run in 64-bit mode.

Solution 4:

You can increase the Heap Size by passing JVM parameters -Xms and -Xmx like below:

For Jar Files:

java -jar -Xms4096M -Xmx6144M jarFilePath.jar

For Java Files:

 java -Xms4096M -Xmx6144M ClassName

The above parameters increase the InitialHeapSize (-Xms) to 4GB (4096 MB) and MaxHeapSize(-Xmx) to 6GB (6144 MB).

But, the Young Generation Heap Size will remain same and the additional HeapSize will be added to the Old Generation Heap Size. To equalize the size of Young Gen Heap and Old Gen Heap, use -XX:NewRatio=1 -XX:-UseAdaptiveSizePolicy params.

java -jar -Xms4096M -Xmx6144M -XX:NewRatio=1 -XX:-UseAdaptiveSizePolicy pathToJarFile.jar

-XX:NewRatio = Old Gen Heap Size : Young Gen HeapSize (You can play with this ratio to get your desired ratio).