You will need the SOA Suite installed for this recipe, and will need permission to execute the domain control scripts, as well as the JVM tools. This recipe assumes that your SOA Suite application is running under a normal load.

The tools jps and jstat are included with both the HotSpot and JRockit JVMs. For brevity, this recipe assumes that you have the relevant bin directory on your path. If you do not, simply use the fully qualified paths to the relevant bin directory.

This recipe assumes you are using HotSpot, as JRockit does not have a permanent generation.

jstat is a JVM tool that can be used to view a number of runtime statistics regarding the JVM. The option –gc prints statistics about garbage collection, including the capacity and utilization of each memory pool. In the preceding example, the parameter –h10 prints the headers every 10 lines, to make the output easier to read, and 2000 is the time in milliseconds between each sample (2 seconds).

Since garbage collection is a "stop the world" activity, any time spent garbage collecting is not the time spent in executing your business logic. We therefore want to minimize the amount of time spent in performing garbage collection. See the chapter on garbage collection for more details on what we are looking to achieve with garbage collection tuning.

In Chapter 5, JVM Garbage Collection Tuning, we also pass the JVM a startup option to enable verbose GC logging output, so we can capture this data all the time.

We can then run free tools such as GCviewer (http://www.tagtraum.com/gcviewer.html) on this data output to visualize the data trends. Later in this chapter, we will introduce using real-time monitoring tools bundled with the JVM to view this same data.