point to note : I'm not a java programmer.
OK that over with I've found the following which may help ....
Making the heap larger decreases the frequency of collections but makes each collection take longer. One good rule of thumb is that you should ensure that there is more than 50% free space available in the heap after a collection. With the -verbosegc flag on, it will print the amount of free space after each collection.
For server applications where swap space and physical memory are not concerns, it may be better to run with a very large heap to spread out the collections. For applications that have a stable heap resident set (i.e., they have a consistent amount of live data after each collection), you can set the initial and maximum heap sizes to be the same value. Setting the heap sizes to be 3-4 times the resident set will put the amount of free heap space in the 65-75% range.
Increasing the startup heap size will cause more system swap to be used. The user will have to balance heap requirements against swap usage. The -ms setting should be high enough that the system is not frantically doing garbage collection, but low enough that system resources are not being consumed too eagerly.
For example, your application needs between 12 and 16 MB. You would want to specify:
-ms32m -mx32m
This would prevent the JVM from trying to fit your app into 1 MB or 4 MB, and would also provide plenty of free space to improve gc performance.
For applications that have a widely varying resident set (or have a different resident set on different runs), try to leave the initial heap size at the default and set the maximum value large enough to handle the largest data set. An example of this kind of application is the Java compiler itself. When compiling small files, it doesn't use much heap space. When compiling lots of files (or very large ones) it uses a lot of space. By keeping the initial heap size low, it doesn't overuse the physical memory of the machine when compiling small files. The tradeoff is that compiling large files will cause the collector to go through some spasms in order to grow the heap to its desired size.
The default is 1 MB.
