Garbage collection (GC) is an essential part of managing memory in modern programming languages. It helps free up unnecessary memory and improve the overall performance of an application. Shenandoah GC is a low-pause garbage collector introduced in OpenJDK that aims to minimize GC pause times while maintaining good throughput.

Though Shenandoah GC provides good out-of-the-box performance, there may be cases where fine-tuning its ergonomics and thresholds can further optimize the GC behavior based on specific application requirements. In this article, we will explore some approaches to fine-tuning Shenandoah GC to achieve better performance.

Table of Contents

• Understanding Ergonomics in Shenandoah GC
  • Throughput, Pause Time, and Garbage Collection
  • GC Ergonomics in Shenandoah
• Fine-tuning Parameters
  • Pause Time Goal
  • Initiating GC Cycle
  • Concurrent GC Threads
• Monitoring and Profiling
  • GC Log Analysis
  • GC Profiling Tools
• Conclusion

Understanding Ergonomics in Shenandoah GC

Throughput, Pause Time, and Garbage Collection

Before diving into the fine-tuning options, let’s briefly explain some key concepts related to GC performance.

Throughput refers to the rate at which an application can execute useful work compared to the total time spent in GC pauses. Higher throughput indicates better performance, as the application spends less time on GC activities.

Pause Time is the duration in which the application is paused for GC activities. Lingering GC pauses can lead to unresponsive or slow applications, especially in interactive or real-time use cases.

Garbage Collection is the process of identifying and freeing up memory occupied by objects no longer needed by the application. This process involves tracing object references, identifying dead objects, and reclaiming the memory occupied by those objects.

GC Ergonomics in Shenandoah

Shenandoah GC employs several techniques to achieve low pause times. It utilizes concurrent marking and relocation, enabling it to perform GC activities concurrently alongside the application threads. This reduces the impact of GC pauses on the application’s responsiveness.

Shenandoah GC also introduces the concept of GC ergonomics, which automatically adjusts various thresholds and parameters based on the application’s behavior and requirements. However, in certain cases, manual fine-tuning can be beneficial to achieve optimal performance.

Fine-tuning Parameters

Here are some parameters you can fine-tune in Shenandoah GC to optimize the GC behavior for your application:

Pause Time Goal

You can set the desired pause time goal for Shenandoah GC. This helps the GC adapt its behavior and strive to keep the pause times within the specified bounds. The default value is set to 10 milliseconds, which is a reasonable goal for most applications. However, you can increase or decrease this value based on your application’s requirements.

-XpauseTarget=<pause_time_in_milliseconds>

Initiating GC Cycle

By default, Shenandoah GC starts a GC cycle when the Java heap is 60% full. However, you can adjust this threshold value to initiate a GC cycle based on your application’s memory allocation patterns. Reducing the threshold can result in shorter pause times, but it may increase the frequency of GC cycles.

-XinitiatingHeapOccupancy=<heap_occupancy_threshold>

Concurrent GC Threads

Shenandoah GC uses multiple threads to perform concurrent marking and relocation. By default, the number of concurrent GC threads is determined automatically based on the available CPU resources. However, you can specify the number of concurrent GC threads manually to ensure optimal utilization of resources.

-XparallelThreads=<number_of_parallel_threads>

Monitoring and Profiling

To determine the effectiveness of the fine-tuning adjustments, you need to monitor and analyze the GC behavior of your application. Here are some approaches:

GC Log Analysis

Enabling the GC log provides valuable insights into the GC behavior, including pause times, heap occupancy, and frequency of GC cycles. Analyzing the GC log can help identify areas for further fine-tuning.

-Xlog:gc*:file=<path_to_gc_log>

GC Profiling Tools

There are several GC profiling tools available for analyzing and visualizing the GC behavior. Tools like jstat, jvisualvm, or commercial tools like Java Mission Control can help you gain a deeper understanding of how Shenandoah GC performs in your application.

Conclusion

Fine-tuning the ergonomics and thresholds of Shenandoah GC can help optimize the performance of your Java application. By adjusting parameters such as pause time goal, initiating GC cycle threshold, and concurrent GC threads, you can achieve lower pause times and improved throughput.

Remember to monitor and analyze the GC behavior using tools like GC logs and profiling tools to evaluate the effectiveness of the fine-tuning adjustments. Keep in mind that the optimal settings may vary depending on the specific characteristics of your application.