Efficient memory management has always been a critical aspect of Java performance, particularly as enterprise applications grow in size and complexity. As the demand for low-latency systems and real-time applications increases, traditional garbage collection (GC) methods struggle to meet these needs. To address this challenge, Java has introduced advanced garbage collection algorithms in recent years. Notably, Z Garbage Collector (ZGC) and Shenandoah are two of the most promising GCs, optimized for low-latency, high-performance applications. In 2025, these collectors continue to evolve, offering substantial improvements in memory management.
This article explores ZGC and Shenandoah, comparing their features and discussing how they enhance Java performance for enterprise applications.
1. Understanding Garbage Collection in Java
Garbage collection is an automatic process in Java that reclaims memory from objects no longer in use, preventing memory leaks and ensuring that the application doesn’t run out of memory. Traditionally, Java used Serial GC, Parallel GC, and CMS (Concurrent Mark-Sweep) collectors, each designed to balance throughput and latency. However, as applications scale, these collectors become less effective, particularly for low-latency and high-concurrency workloads.
The introduction of ZGC and Shenandoah addresses these challenges by offering low-latency garbage collection with continuous performance improvements, particularly in environments where real-time processing is crucial, such as financial services, healthcare, and gaming.
1.1 Z Garbage Collector (ZGC)
ZGC is a low-latency garbage collector introduced in Java 11 as an experimental feature and further enhanced in subsequent Java versions. It is designed to minimize pause times, making it an ideal choice for applications requiring high responsiveness, such as real-time systems and microservices.
Key Features of ZGC:
- Concurrent Mark and Compact Phases: ZGC performs most of its work concurrently with the application threads, significantly reducing the duration of GC pauses. Even large heaps, often exceeding 100 GB, can be managed without significant application disruption.
- Low-Latency Design: ZGC’s goal is to keep GC pause times below 10 milliseconds, regardless of heap size. This is achieved by using techniques such as region-based memory management and colored pointers, allowing for almost non-blocking GC operations.
- Scalability: ZGC is designed to handle large heaps, making it suitable for modern, memory-intensive applications. It can scale to multi-terabyte heaps, where traditional GCs may struggle.
- Garbage Collection with Less Impact: Unlike traditional GCs, which stop the world (pause all application threads for GC), ZGC ensures that the pause times are shorter and predictable, helping maintain a smooth application experience.
When to Use ZGC:
- High-throughput, low-latency systems (e.g., real-time trading systems, gaming backends)
- Applications with large heap sizes (greater than 100 GB)
- Systems that require predictable and consistent GC pause times
Challenges with ZGC:
- Resource Intensive: ZGC consumes more resources, particularly CPU, during GC cycles due to concurrent processing.
- Newer GC: As a relatively new GC, it may not yet have the same level of maturity as older collectors like G1, especially in complex production environments.
1.2 Shenandoah Garbage Collector
Introduced in Java 12, Shenandoah is another low-latency garbage collector aimed at reducing pause times while maintaining high throughput. It was initially developed by Red Hat for use in enterprise environments but has since become an integral part of Java’s GC landscape.
Key Features of Shenandoah:
- Concurrent Mark and Sweep Phases: Similar to ZGC, Shenandoah runs most of its GC phases concurrently with application threads. However, unlike ZGC, it focuses more on the pause time rather than the absolute size of the heap.
- Pause-Time Control: Shenandoah aims to reduce GC pause times to below 10 ms by conducting major GC activities concurrently. Its goal is to keep applications responsive, even in the face of memory management tasks.
- Heap Region Management: Shenandoah uses a region-based heap model, where memory is divided into regions for more efficient collection and management. This enables quick reclamation of memory without stopping the application for long periods.
- Low Overhead: Shenandoah is designed to work efficiently with heaps of various sizes, including medium and large-sized heaps, with minimal impact on CPU resources.
When to Use Shenandoah:
- Applications requiring consistent pause-time control, such as high-frequency trading systems, real-time data processing applications, and microservices
- Systems where heap size is moderate to large, and minimizing GC pause times is crucial
- Enterprise systems built on Red Hat or JVM-based infrastructure
Challenges with Shenandoah:
- GC Efficiency: Shenandoah’s low pause time comes at the expense of a slight decrease in throughput compared to G1 and Parallel GC.
- Initial Overhead: For smaller heap sizes, Shenandoah may have higher memory overhead due to its concurrent nature.
2. Comparison of ZGC and Shenandoah
| Feature | ZGC | Shenandoah |
|---|---|---|
| Pause Times | Sub-10 ms (target) | Sub-10 ms (target) |
| Heap Size | Works best with large heaps (100 GB+) | Best suited for medium to large heaps |
| Throughput | Slightly lower due to concurrent processing | Good throughput with low pause times |
| Concurrent Phases | Mark and Compact | Mark and Sweep |
| Latency | Very low, designed for real-time systems | Low, designed for low-latency environments |
| Best Use Case | Real-time systems, large heaps | Enterprise systems, microservices |
3. Choosing the Right GC for Your Application
- ZGC is ideal if your application demands low-latency and works with large heaps (hundreds of GBs or more). It shines in environments that require real-time responsiveness, such as financial services, gaming, or data analytics.
- Shenandoah, while also optimized for low-latency operations, is better suited for systems with moderate heap sizes or applications that require consistent and predictable GC pause times. It’s particularly well-suited for enterprise applications, microservices, and containerized environments.
Both collectors are built to meet the needs of modern Java applications, offering substantial improvements in performance, scalability, and responsiveness over older garbage collection methods.
4. Conclusion
The introduction of ZGC and Shenandoah in Java provides developers with powerful tools for optimizing memory management, particularly in low-latency and high-throughput environments. Whether you’re building an enterprise-level Java application or a real-time system, understanding the differences and strengths of these new garbage collectors is crucial to achieving optimal performance. By choosing the right GC, you can ensure that your application scales efficiently, remains responsive under load, and handles large datasets without GC-induced performance bottlenecks.
In 2025, as these collectors continue to evolve, Java will remain a strong contender in the world of high-performance computing, ensuring that developers can meet the ever-growing demands of modern enterprise applications.
