Would using -Xxmn option speed up an xpath/DOM application

Question

A developer mentioned in another thread
"You can increase the default maximum heap size. Different OSes and JVM/versions have an upper limit for this.
For the Sun JVM the command line option is doc'd in the docs. It is "-Xmxn" where n is replaced with something like "80m". The default size is 64m (meg) for 1.3 ."
My question is would using the -Xxmn speed up a java application using xpath and DOM or no?

Answer 1

This may speed it up if the amount of time spent garbage collecting is getting too high. As you raise the size of a heap it has to garbage collect less often given a fixed rate of allocations per unit time. Unfortunately, the time it takes to GC also rises a bit with a large heap, so your mileage may vary.
Take a look at the rate at which you are GC'ing. use -verbose:gc to do that.
Also, raising -XmsNNm (NN is number of megs) to raise the initial heap size can also help improve startup speed. This should be either the like amount of memory you need or some reasonable fraction of the maximum heap size (perhaps == to the max heap size). This will eliminate extra GC's and time spent to grow the heap as the application runs.
If you are GC'ing fairly often (every few to 10 seconds) and the GC's take a fair amount of time (consistently greater than .5 to 1 seconds), you might want to further tune the heap. For Sun and Java 1.3.1, I often use something like this to run large programs and J2EE servers (the exact numbers may vary:
java -server -Xms256m -Xmx512m -XX:NewSize=128m -XX:MaxNewSize=128m -XX:SurvivorRatio=2
Take a look at this: http://java.sun.com/docs/hotspot/index.html
Chuck