Table of Contents
Introduction
Shenandoah GC is a low-pause garbage collector designed for applications with large heaps. It aims to reduce long pause times and improve overall throughput. However, like any garbage collector, it can encounter issues that impact application performance. In this blog, we will discuss some common issues that can arise with Shenandoah GC and provide troubleshooting techniques to resolve them.
Common Issues
High Memory Usage
One potential issue you might encounter with Shenandoah GC is high memory usage. This can happen if the garbage collector is not able to reclaim memory efficiently, leading to increased heap size. To address this problem, you can try the following troubleshooting techniques:
- Monitor Memory Consumption: Use tools like Java Flight Recorder or VisualVM to monitor the memory usage of your application over time. Look for abnormal spikes or consistently high memory usage.
- Analyze Object Retention: Analyze the objects retained in memory using a memory profiler to understand why they are not being garbage collected. Make sure you are not holding references to objects unnecessarily.
Long GC Pauses
Another common issue is long garbage collection pauses. These pauses occur when Shenandoah GC needs to perform certain operations that can’t be done concurrently. To mitigate long GC pauses, consider the following troubleshooting techniques:
- Analyze GC Logs: Enable verbose GC logging and analyze the logs to identify the root cause of long pauses. Look for stop-the-world phases in the logs and investigate the operations performed during these pauses.
- Tune GC Parameters: Adjust the garbage collector parameters such as heap size, thread count, and GC cycle time to achieve a balance between throughput and pause times.
- Consider Concurrent Mark Phases: The length of concurrent marking phases can impact GC pauses. Experiment with different concurrent marking threads to find the optimal balance.
Concurrent Mode Failure
Concurrent mode failure is an issue where Shenandoah GC is unable to complete garbage collection concurrently and falls back to the traditional stop-the-world mode. This can significantly impact pause times and throughput. To troubleshoot concurrent mode failure, you can:
- Check GC Logs: Examine the GC logs for concurrent mode failure messages. This will help identify the cause, such as insufficient memory or high promotion failure.
- Increase Heap Size: If the logs indicate low memory availability during concurrent mode, consider increasing the heap size to provide more memory for the garbage collector.
- Fine-tune Concurrent Mode Settings: Adjust the concurrent mode settings such as
-XX:ShenandoahOptimizeInitialMarkand-XX:ShenandoahOptimizeFinalMarkto improve concurrent marking performance.
Troubleshooting Techniques
Monitor Memory Consumption
To monitor memory consumption, use tools like Java Flight Recorder or VisualVM. Monitor the heap usage and look for any abnormal spikes or consistently high memory usage. Analyze the objects retained in memory to identify potential memory leaks or excessive object allocations.
Analyze GC Pauses
Enable verbose GC logging and analyze the GC logs to understand the duration and frequency of garbage collection pauses. Look for any stop-the-world phases and investigate the operations performed during those pauses. Adjust the GC parameters based on the analysis to optimize pause times.
Check Concurrent Mode Failure
Check the GC logs for concurrent mode failure messages. These messages indicate when Shenandoah GC was unable to complete garbage collection concurrently and had to fall back to stop-the-world mode. Identify the cause of the failure, such as insufficient memory or high promotion failure. Adjust the heap size and fine-tune concurrent mode settings accordingly.
Conclusion
Shenandoah GC is a powerful garbage collector that can significantly improve performance for applications with large heaps. However, it’s important to be aware of common issues and have troubleshooting techniques in place to resolve them. By monitoring memory consumption, analyzing GC pauses, and addressing concurrent mode failure, you can ensure optimal performance of your application with Shenandoah GC.
#gc #garbagecollector