How do I set Java's min and max heap size through environment variables?

Question

How do I set Java\'s min and max heap size through environment variables?

I know that the heap sizes can be set when launching java, but I would like to have this ad

Answer 1

A couple of notes:

1. Apache ant doesn't know anything about JAVA_OPTS, while Tomcat's startup scripts do. For Apache ant, use ANT_OPTS to affect the environment for the JVM that runs /ant/, but not for the things that ant might launch.

2. The maximum heap size you can set depends entirely on the environment: for most 32-bit systems, the maximum amount of heap space you can request, regardless of available memory, is in the 2GiB range. The largest heap on a 64-bit system is "really big". Also, you are practically limited by physical memory as well, since the heap is managed by the JVM and you don't want a lot of swapping going on to the disk.

3. For server environments, you typically want to set -Xms and -Xmx to the same value: this will fix the size of the heap at a certain size and the garbage collector has less work to do because the heap will never have to be re-sized.