Garbage collection (GC) is a critical process in Java applications for managing memory and reclaiming unused objects. However, traditional GC algorithms, such as the Concurrent Mark Sweep (CMS), can lead to significant pause times, causing performance issues in applications with large heaps.
To address this problem, the Shenandoah GC was introduced by Red Hat as part of OpenJDK. Shenandoah is designed to reduce pause times without sacrificing application throughput. In this article, we will explore how Shenandoah GC accomplishes this and its benefits for Java applications.
Understanding Pause Times
Pause times refer to the intervals during which Java application execution is halted for garbage collection. The longer the pause, the more disruption it can cause to the application’s responsiveness and overall performance. High pause times can hinder real-time systems, large-scale applications, and microservices.
Traditional GC algorithms, like CMS, typically have pause times proportional to the heap size. As the heap grows, the pauses become longer, affecting application responsiveness. Shenandoah GC, on the other hand, aims to keep pause times short and independent of the heap size.
Concurrent Garbage Collection
Shenandoah GC achieves low pause times by adopting a concurrent garbage collection approach. It performs garbage collection concurrently with the running Java threads, minimizing the impact on application responsiveness. This is in contrast to the stop-the-world approach used by CMS and other traditional GC algorithms.
During the concurrent phase, Shenandoah GC performs garbage collection work while the application threads continue execution. It uses snapshot-at-the-beginning (SATB) technique to keep track of object modifications made by Java threads during the concurrent phase. This ensures that all objects referenced are correctly handled during garbage collection.
Compacting Concurrently
In addition to performing garbage collection concurrently, Shenandoah GC also performs compaction concurrently. Compaction is the process of rearranging objects in memory to reclaim fragmented memory and improve memory locality. Traditionally, compaction requires stopping the application threads, leading to pause times proportional to the size of the heap.
Shenandoah GC takes a different approach by compacting concurrently. It moves objects around in memory while the application threads continue to execute. By doing so, it eliminates the need for lengthy pause times caused by compaction, resulting in consistently low and predictable pause times.
Benefits for Java Applications
Shenandoah GC offers several benefits for Java applications:
-
Low Latency: By reducing pause times and making them independent of heap size, Shenandoah GC ensures that Java applications remain responsive and meet strict performance requirements.
-
Predictability: With Shenandoah GC, pause times are consistent and predictable, allowing for better performance tuning and optimization.
-
Scalability: Shenandoah GC’s concurrent approach allows it to scale well with modern multi-core processors, making it suitable for large-scale applications that require high throughput.
-
Compatibility: Shenandoah GC is part of OpenJDK and integrates with familiar Java tools, making it easy to adopt in existing Java applications.
In conclusion, Shenandoah GC significantly improves pause times in Java applications by adopting a concurrent garbage collection approach and performing compaction concurrently. By keeping pause times low and predictable, Shenandoah GC ensures better performance and responsiveness, making it a valuable addition to the Java GC ecosystem.
To learn more about Shenandoah GC, check out the official documentation and try it out in your Java applications today.
Tags: #ShenandoahGC #JavaGC