Increase heap size in Java

Question

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)?

Answer 1

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

Answer 2

java -d64 -Xms512m -Xmx4g HelloWorld

where, -d64: Will enable 64-bit JVM -Xms512m: Will set initial heap size as 512 MB -Xmx4g: Will set maximum heap size as 4 GB (here java file name is : HelloWorld.java)

Answer 3

Please use below command to change heap size to 6GB

export JAVA_OPTS="-Xms6144m -Xmx6144m -XX:NewSize=256m -XX:MaxNewSize=356m -XX:PermSize=256m -XX:MaxPermSize=356m"

Answer 4

Yes. You Can.

You can increase your heap memory to 75% of physical memory (6 GB Heap) or higher.

Since You are using 64bit you can increase your heap size to your desired amount. In Case you are using 32bit it is limited to 4GB.

$ java -Xms512m -Xmx6144m JavaApplication

Sets you with initial heap size to 512mb and maximum heapsize to 6GB.

Hope it Helps.. :)

Answer 5

Can I increase the heap memory to 75% of physical memory(6GB Heap).

Yes you can. In fact, you can increase to more than the amount of physical memory, if you want to.

Whether it is a good idea to do this depends on how much else is running on your system. In particular, if the "working set" of the applications and services that are currently running significantly exceeds the available physical memory, your system is liable to "thrash", spending a lot of time moving virtual memory pages to and from disk. The net effect is that the system gets horribly slow.

Answer 6

You can increase to 4GB 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.