Java 21’s Enhanced ZGC: A Performance Deep Dive

Java 21 introduces significant enhancements to the Z Garbage Collector (ZGC), building upon its already impressive low-latency performance. This post dives deep into these improvements and explores their impact on application performance.

ZGC: A Quick Recap

ZGC, or Z Garbage Collector, is a scalable, low-latency garbage collector designed for large heaps. Its key features include:

• Concurrent operations: Most GC operations happen concurrently with application threads, minimizing pauses.
• NUMA-awareness: Optimized for Non-Uniform Memory Access architectures for improved performance on multi-socket systems.
• Support for massive heaps: Handles heaps exceeding 16TB.

Java 21’s ZGC Enhancements

Java 21 focuses on further refining ZGC’s performance and stability. Key improvements include:

Improved Throughput

While ZGC excels at low-latency, Java 21 aims to boost its throughput. This is achieved through various optimizations in the GC’s internal algorithms, resulting in faster garbage collection cycles and reduced overall overhead.

Reduced Memory Footprint

ZGC’s memory footprint has been reduced, meaning less memory is consumed by the garbage collector itself. This frees up more resources for the application, leading to better performance and potentially allowing for larger heaps on systems with limited RAM.

Enhanced Stability and Reliability

Java 21 also includes bug fixes and improvements to the stability and robustness of ZGC. This reduces the risk of unexpected pauses or crashes, leading to more reliable applications.

Performance Benchmarks

While specific benchmark results vary based on hardware and application characteristics, general observations from early testing indicate:

• Significant reduction in pause times: Even shorter pauses compared to previous ZGC versions.
• Improved throughput in certain workloads: Especially noticeable in applications with high object allocation rates.
• Lower memory consumption: Leading to more efficient resource utilization.

It’s recommended to conduct your own benchmarks to assess the performance impact on your specific application and workload.

Enabling ZGC

Enabling ZGC in Java 21 is straightforward. You can use the following JVM flag:

-XX:+UseZGC

You can add this flag to your application’s startup command.

Conclusion

Java 21’s enhanced ZGC represents a significant step forward in garbage collection technology. The improvements in throughput, memory footprint, and stability make it an even more compelling option for applications requiring low-latency and high-performance characteristics. The enhancements contribute towards making Java applications more responsive, efficient, and reliable, especially on large-scale deployments.