In today’s blog post, we will be exploring how to fine-tune the concurrent cycle duration with the Shenandoah garbage collector (GC). The Shenandoah GC is a low-pause, concurrent garbage collector for the Java Virtual Machine (JVM) that aims to minimize pause times and ensure high application performance. Fine-tuning the concurrent cycle duration can help optimize the garbage collection process and further reduce pause times. Let’s dive in!

Table of Contents

• Understanding Concurrent Cycle Duration
• Fine-Tuning Concurrent Cycle Duration
• Conclusion

Understanding Concurrent Cycle Duration

The concurrent cycle duration refers to the time it takes for the Shenandoah GC to complete a garbage collection cycle while allowing the application threads to run simultaneously. The GC work is divided into multiple phases, such as the initial mark, concurrent marking, final mark, and concurrent evacuation.

By default, the Shenandoah GC dynamically adjusts the concurrent cycle duration based on the heap size and the number of available CPU cores. However, you can fine-tune this duration to better suit your application’s needs and reduce the GC pause times even further.

Fine-Tuning Concurrent Cycle Duration

To fine-tune the concurrent cycle duration, you can use the following JVM options:

1. ShenandoahGCHeuristics: This option accepts different values to control the concurrent cycle duration. By default, it uses adaptive, which automatically adjusts the cycle duration based on available CPU cores and heap sizes. You can set it to aggressive to shorten the concurrent cycle duration at the expense of higher CPU and memory utilization. Alternatively, you can set it to conservative to increase the concurrent cycle duration, allowing more time for application threads but potentially increasing GC pause times.

    java -XX:+UnlockExperimentalVMOptions -XX:+UseShenandoahGC -XX:ShenandoahGCHeuristics=aggressive MyApp
   

2. ShenandoahUncommitDelay: This option controls the duration, in milliseconds, that the GC waits before uncommitting memory. By default, it is set to 100 milliseconds. You can increase this value to delay memory uncommit, resulting in longer concurrent cycles but potentially reducing fragmentation.

    java -XX:+UnlockExperimentalVMOptions -XX:+UseShenandoahGC -XX:ShenandoahUncommitDelay=200 MyApp
   

3. ShenandoahGCMode: This option allows you to select the GC mode that affects the concurrent cycle duration. The available modes include iu(in-use) and du(dead-use). The iu mode prioritizes concurrent work, whereas the du mode prioritizes reclaiming memory. By default, it uses iu.

    java -XX:+UnlockExperimentalVMOptions -XX:+UseShenandoahGC -XX:ShenandoahGCMode=du MyApp
   

Experiment with these options and measure their impact on the GC pause times and overall application performance. Fine-tuning the concurrent cycle duration requires observation and careful consideration of your application’s characteristics and requirements.

Conclusion

Fine-tuning the concurrent cycle duration with the Shenandoah GC can help reduce the pause times even further and optimize the garbage collection process for your Java application. By adjusting the Shenandoah GC heuristics, uncommit delay, and GC mode, you can find the right balance between pause times and application performance. Experiment with these options in your environment and benchmark the results to achieve the best possible configuration. #GCoptimization #Java