Calculating Java Heap Size for Identity Manager implementation

How do we determine the Java Heap Size to be set on Sun Application server for a typical Identity Manager deployment?

This is the typical java heap size setting used for most of the projects which I have implemented in Sun Identity Manager on Solaris Platform


Assume that Physical Memory of Solaris = 4GB
Assume the memory used by OS = 256 MB

Java Heap size that should be set should be equivalent to 80% of remaing memory left.

((4096 - 256) * 0.8 = 3072)

The formula is

Java Hep size = (Physical Memory-Memory used by OS)*.8