Shenandoah is a low-pause time garbage collector (GC) algorithm developed by Red Hat for the OpenJDK platform. It aims to reduce pause times during GC cycles and improve application performance. However, like any GC algorithm, there may be situations where you need to debug or profile the Shenandoah GC to identify issues or optimize its behavior.

In this blog post, we will explore some techniques for debugging and profiling the Shenandoah GC algorithm.

1. Verbose Logging

Shenandoah provides a set of logging options that can help you understand the behavior of the GC algorithm. Enabling verbose logging can provide you with valuable information about GC cycles, heap usage, and other performance-related metrics.

To enable verbose logging for Shenandoah GC, add the following JVM flag to your application launch command:

-Xlog:gc+shenandoah*=debug

This will enable logging for Shenandoah GC at the debug level. You can adjust the log level and specific log tags according to your requirements.

2. GC Logs

GC logs are an essential tool for understanding how the GC algorithm is behaving. Shenandoah GC provides detailed information in its logs, including heap utilization, pause times, and other GC-related events.

To enable GC logging for Shenandoah, use the following JVM flags:

-XX:+UnlockDiagnosticVMOptions -XX:+PrintGC -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintAdaptiveSizePolicy

This will print the GC events to the console or a specified log file, depending on your logging configuration.

3. GC Profiling

Profiling the Shenandoah GC can help identify performance bottlenecks and optimize your application’s memory usage. There are various profiling tools available that can assist you in this process.

One such tool is Java Flight Recorder (JFR), which provides detailed insights into the memory usage and GC behavior of your application. You can enable JFR by adding the following JVM flags:

-XX:+UnlockCommercialFeatures -XX:+FlightRecorder

Once JFR is enabled, it will generate a recording file that can be analyzed using tools like Java Mission Control or third-party profilers like VisualVM.

Another useful profiling tool is Async-profiler, which is a low-overhead sampling profiler for Java applications. It can provide detailed CPU and memory profiling information, including GC activity. You can find the Async-profiler on GitHub and follow the instructions to use it with Shenandoah GC.

Conclusion

Debugging and profiling the Shenandoah GC algorithm can help you identify and resolve performance-related issues in your Java applications. Leveraging verbose logging, GC logs, and profiling tools like JFR and Async-profiler can provide valuable insights into the GC behavior and memory usage of your application.

By understanding how Shenandoah GC works and using the appropriate debugging and profiling techniques, you can optimize its performance and minimize pause times, leading to improved application responsiveness. #debugging #profiling