Table of Contents
Introduction
Shenandoah is an advanced garbage collector (GC) algorithm available in OpenJDK, designed to reduce GC pause times for large heaps. It achieves this by performing concurrent collection, meaning that the GC work is done concurrently with the running Java application. In this article, we will explore two techniques to fine-tune the performance of Shenandoah GC: adjusting the number of concurrent GC threads and optimizing work stealing.
Fine-tuning Concurrent GC Threads
The number of concurrent GC threads determines the amount of parallelism during GC cycles. By default, Shenandoah GC will dynamically adjust the number of GC threads based on the number of available processor cores. However, in some cases, it may be necessary to manually configure the number of threads to achieve optimal performance.
To specify the number of concurrent GC threads, you can use the -XX:ParallelGCThreads flag. For example, to set the number of threads to 8, add the following flag when starting your Java application:
java -XX:ParallelGCThreads=8 -XX:+UseShenandoahGC <your_application>
It is important to note that the optimal number of threads depends on the specific workload and hardware setup. Experimentation and monitoring GC behavior can help determine the ideal number of concurrent GC threads for your application.
Fine-tuning Work Stealing
Work stealing is a mechanism used by Shenandoah GC to balance the workload across concurrent GC threads. When a thread completes its work, it can steal tasks from other threads to prevent them from becoming idle.
To fine-tune work stealing behavior, you can use the -XX:ShenandoahWorkStealingMode flag. There are three available modes:
- adaptive (default) - Allows work stealing when it is beneficial and disables it when the workload is low.
- always - Enables work stealing unconditionally. This can improve overall throughput but may slightly increase GC pause times.
- never - Disables work stealing completely.
To set the work stealing mode to “always”, add the following flag when starting your Java application:
java -XX:ShenandoahWorkStealingMode=always -XX:+UseShenandoahGC <your_application>
The optimal work stealing mode depends on factors like the number of concurrent GC threads, workload characteristics, and application requirements. Experimentation and measurement are recommended to determine the most suitable mode for your use case.
Conclusion
Fine-tuning concurrent GC threads and work stealing can significantly impact the performance of Shenandoah GC. By adjusting the number of threads and optimizing work stealing behavior, you can reduce GC pause times and improve the overall throughput of your Java application. Experimentation, monitoring, and measuring the GC behavior are crucial steps in finding the optimal configuration for your specific workload and hardware setup.
#hashtags: #ShenandoahGC #GarbageCollection