Garbage collection is an important aspect of memory management in Java applications. It aims to automatically reclaim memory that is no longer in use by the application. The Java Virtual Machine (JVM) comes with different garbage collectors, each with its own strengths and weaknesses.

One of the garbage collectors available in the HotSpot JVM is Shenandoah GC. It is designed to reduce pause times and maintain good application throughput even with large heaps. In this blog post, we will explore the features and benefits of Shenandoah GC.

Table of Contents

• What is Shenandoah GC?
• How Shenandoah GC Works
• Key Features of Shenandoah GC
• Benefits of Using Shenandoah GC
• Conclusion

What is Shenandoah GC?

Shenandoah GC is a low-pause garbage collector introduced in JDK 12. It is specially designed to minimize pause times and meet the requirements of modern applications. Unlike traditional garbage collectors, such as the Concurrent Mark Sweep (CMS) collector, Shenandoah GC focuses on concurrent evacuation - a technique that allows objects to be moved while the application continues to execute.

How Shenandoah GC Works

Shenandoah GC introduces a novel approach to memory management called “Region-based Garbage Collection”. Instead of dividing the heap into two spaces like the CMS collector, Shenandoah GC divides the heap into regions. Each region is further divided into sub-regions, containing both live and garbage objects. The key idea is to allow concurrent marking and evacuation of objects within individual sub-regions, minimizing the impact on the application’s throughput.

Key Features of Shenandoah GC

• Concurrent Marking: Shenandoah GC performs the marking phase concurrently with the application’s execution, reducing pause times to a minimum. It uses a technique called “precise” marking, which ensures that only live objects are marked and evacuated, resulting in better performance.
• Concurrent Evacuation: Shenandoah GC uses concurrent evacuation to move live objects to free regions. This allows the application to continue running while objects are being evacuated, reducing pause times even further.
• Compaction-free: Shenandoah GC is a compaction-free garbage collector, meaning it does not move all live objects to achieve memory compaction. Instead, only live objects that need to be evacuated are moved, resulting in shorter pause times and improved throughput.
• Low Latency: The main goal of Shenandoah GC is to minimize pause times. It achieves this by performing most of its work concurrently with the application, leading to very low latency and improved responsiveness.
• Scalability: Shenandoah GC is designed to scale with the number of available CPU cores. It utilizes parallel and concurrent phases to take advantage of multicore systems, making it suitable for modern hardware architectures.

Benefits of Using Shenandoah GC

• Reduced Pause Times: The primary benefit of Shenandoah GC is a significant reduction in garbage collection pause times. This makes it suitable for applications with strict latency requirements, such as real-time systems or low-latency trading platforms.
• Improved Application Throughput: By performing most of the work concurrently, Shenandoah GC allows applications to maintain good throughput even with large heaps. This is particularly important for applications that handle a high volume of data.
• Better Responsiveness: With low pause times, Shenandoah GC ensures better responsiveness of the application. Users will experience smoother interactions and reduced lag, resulting in an improved user experience.
• Memory Efficiency: Shenandoah GC minimizes memory fragmentation and keeps the application’s memory usage efficient by using region-based garbage collection and concurrent evacuation.

Conclusion

Shenandoah GC is a promising garbage collector for Java applications that require low pause times and improved throughput. Its concurrent marking and evacuation approach, combined with compaction-free techniques, make it a viable option for modern applications. By minimizing pause times and maintaining good application responsiveness, Shenandoah GC enhances the overall user experience. As JVMs continue to evolve, Shenandoah GC stands as a valuable addition to the list of garbage collectors available to Java developers.

#java #GC