In recent years, garbage collection (GC) algorithms have seen significant improvements to better manage the growing memory requirements of applications. One such advanced GC algorithm is Shenandoah, which aims to shorten the pause times of GC operations while maintaining excellent throughput.

One of the key factors in determining pause times during GC is the duration of the parallel phase. The parallel phase is the phase where multiple threads work together to perform GC tasks in parallel, such as marking objects and reclaiming garbage. Configuring the duration of this phase is essential for achieving a good balance between pause times and overall application performance.

In this article, we’ll explore how to fine-tune the parallel phase duration in Shenandoah GC to optimize GC pause times for your application.

Understanding the parallel phase

The parallel phase in Shenandoah GC consists of multiple stages, including root scanning, concurrent marking, cleanup, and concurrent evacuation. The goal of the parallel phase is to make efficient use of multiple threads to perform these stages in parallel, thus reducing the overall GC pause time.

However, the parallel phase should not be too short, as it can lead to increased pause times due to increased synchronization overhead. On the other hand, making it too long can impact the application’s throughput and responsiveness. Therefore, finding the right duration for the parallel phase is crucial.

Configuring the parallel phase duration

Shenandoah GC provides a configurable option, ShenandoahParallelPhaseTime, that allows you to set the desired duration for the parallel phase. This option is specified in milliseconds and can be adjusted based on your application’s requirements.

To fine-tune the parallel phase duration, follow these steps:

1. Analyze your application’s GC logs to understand the current pause times and overall GC behavior.
2. Start with the default value for ShenandoahParallelPhaseTime and observe the impact on GC pause times.
3. Increase or decrease the value gradually based on your observations. If you notice excessive pause times, decrease the duration; if the pause times are already short but the throughput is affected, consider increasing the duration.

Remember that the optimal duration may vary depending on your application’s workload, hardware setup, and overall performance goals. It is essential to measure the impact of each configuration change to find the best balance.

Monitoring and validating the changes

To monitor the impact of your changes to the parallel phase duration, you can enable GC logging and monitor the pause times, allocation rate, and overall throughput. Additionally, you can use profiling tools and application metrics to validate whether the changes have a positive effect on the application’s performance.

Always make sure to test your changes in a representative production-like environment to ensure accurate results. Benchmarking your application with different parallel phase durations can help you determine the optimal configuration for your specific use case.

Conclusion

Fine-tuning the parallel phase duration in Shenandoah GC can significantly improve the pause times of garbage collection operations in your Java application. By carefully adjusting the ShenandoahParallelPhaseTime option and monitoring the impact, you can achieve a good balance between pause times and overall application performance.

Remember that finding the optimal configuration may require some experimentation and adjustment based on your specific workload and performance goals. With the right configuration, your application can benefit from reduced GC pause times and improved responsiveness.

#gc #garbagecollection