Memory fragmentation can be a challenging issue in garbage-collected languages like Java. As objects are allocated and deallocated dynamically, memory can become fragmented, leading to inefficient memory utilization and increased garbage collection overhead.
In this article, we will explore how the Shenandoah Garbage Collector (GC) in Java addresses the problem of memory fragmentation and improves the overall performance of the application.
What is Shenandoah GC?
Shenandoah GC is a low-pause, concurrent garbage collector introduced in Java 12. It is designed to reduce pause times and improve scalability by enabling the concurrent collection of the entire heap, including both the young and old generations. Shenandoah GC employs several novel techniques to achieve these goals, including concurrent compaction and load barriers.
Fragmentation in Garbage-Collecting Systems
Memory fragmentation occurs when memory is allocated and deallocated in a non-contiguous manner, resulting in the formation of small, unusable memory chunks. This fragmentation can occur in both the young and old generations of the Java heap.
Fragmentation can have several negative effects on the performance of a garbage-collected system:
- Increased memory usage: Fragmentation reduces memory utilization efficiency as usable memory is scattered across small chunks.
- Longer garbage collection pauses: Fragmentation can enlarge the managed heap, resulting in longer garbage collection pauses, as the GC needs to scan a larger memory space.
- Memory allocation failures: Fragmentation can cause memory allocation failures even when sufficient memory is available, as the required contiguous memory cannot be found.
Addressing Fragmentation with Shenandoah GC
Shenandoah GC employs a concurrent compaction technique to address fragmentation. During the concurrent phase, it identifies fragmented regions in the heap and compacts them in the background, without stopping the application threads. This compaction process helps to reduce fragmentation and improve memory utilization.
Additionally, Shenandoah GC uses specialized load barriers to handle concurrently access objects during the compaction phase. These load barriers ensure that objects are accessed correctly, even while the heap is being compacted. By allowing concurrent compaction and load barriers, Shenandoah GC minimizes the impact on application throughput and reduces pause times.
Benefits of Shenandoah GC
The use of Shenandoah GC in Java offers several benefits, especially when dealing with applications that require low latency and high scalability:
- Reduced pause times: Shenandoah GC significantly reduces pause times by allowing concurrent garbage collection and compaction.
- Improved scalability: By concurrently garbage collecting the entire heap, Shenandoah GC improves the scalability of applications, enabling better performance even under heavy workloads.
- Better memory utilization: The compaction process in Shenandoah GC helps to reduce fragmentation and improve memory utilization efficiency, resulting in more available memory for the application.
- Low application throughput impact: The concurrent nature of Shenandoah GC and the use of load barriers ensure minimal impact on application throughput, enabling better responsiveness.
Conclusion
Memory fragmentation is a common challenge in garbage-collected languages like Java. Shenandoah GC addresses this issue by employing concurrent compaction and load barriers, providing reduced pause times, improved scalability, and better memory utilization.
By leveraging Shenandoah GC, Java developers can enhance the performance of their applications, especially in scenarios where low latency and high scalability are crucial. So, if you’re working on a Java application with these requirements, give Shenandoah GC a try and see the improvements it brings to your application’s garbage collection process.
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