Optimizing your JVM for Best Performance

The better your JVM performs, the better your installation of Tomcat will perform. It's as simple as that. Getting the most out of your JVM is a matter of configuring its settings to match your real-world performance needs as closely as possible. Update your JVM to the latest version, establish some accurate benchmarks so you have a way of quantifying any changes you make, and then get down to business.

Effective Memory Management

The main thing to consider when tuning your JVM for Tomcat performance is how to avoid wasting memory and draining your server's power to process requests. Certain automatic JVM processes, such as garbage collection and memory reallocation, can chew through memory if they occur more frequently than necessary. You can make sure these processes only occur when they need to by using the JAVA_OPTS -Xmx and -Xms switches to control how JVM handles its heap memory.

If your JVM is invoking garbage collection too frequently, use the -Xmx switch to start the JVM with a higher maximum heap memory. This will free up CPU time for the processes you really care about.

Configuring Threads

Next, let's take a look at the way your JVM handles threads. There are two types of Java threads - green and native. Native threads are scheduled by your OS, while green threads are managed entirely within the user space of your Java Virtual Machine. If your JVM supports both, you should try both models to determine the best choice for your site.

Generally, native threads offer the best performance, especially if you are running a lot of I/O bound applications (which is very likely, since you are running Tomcat). However, green threads outperform native threads in some specific areas, such as synchronization and thread activation. Try both and see which option gives you the biggest performance boost.

Managing Your JVM

Tuning for performance is not a finite process. Usage situations change over time, and problems that are not immediately apparent can expose themselves over a longer period of time. There are a number of tools available to help you keep an eye on your JVM's performance.

One of the most convenient solution is VisualVM, a tool that is packaged with the JDK, and can provide you with great performance statistics. Other commonly used JVM monitoring tools included with the SDK include console, jps, and jstack. Run regular tests on your JVM to make sure its configuration still suits your needs, and you can be sure that your Tomcat instances will always perform at their best!