Garbage collection (GC) plays a crucial role in Java’s memory management by automatically reclaiming unused objects and preventing memory leaks. However, selecting the right garbage collector can significantly impact an application’s performance, affecting response time, throughput, and memory usage. In this article, we will explore different garbage collectors in Java, their use cases, and how to choose the best one for optimal performance.

Understanding Java Garbage Collection

Garbage collection in Java is managed by the Java Virtual Machine (JVM). The JVM automatically removes objects that are no longer needed, freeing up memory for new allocations. However, different applications have different performance requirements, necessitating the choice of an appropriate GC algorithm.

Types of Garbage Collectors in Java

Java provides several garbage collectors, each designed to optimize performance based on workload characteristics. The main garbage collectors include:

1. Serial Garbage Collector
2. Parallel Garbage Collector
3. G1 (Garbage First) Garbage Collector
4. Z Garbage Collector (ZGC)
5. Shenandoah Garbage Collector
6. Epsilon Garbage Collector

Let’s explore each of them in detail.

1. Serial Garbage Collector

The Serial GC is a simple, single-threaded garbage collector best suited for small applications and single-core processors.

Characteristics:

• Uses a single thread for garbage collection.
• Stops the application during garbage collection (stop-the-world events).
• Best for simple applications with low memory requirements.

Use Case:

• Suitable for small desktop applications or embedded systems with limited CPU power.

How to enable it:

java -XX:+UseSerialGC -jar MyApp.jar

2. Parallel Garbage Collector

The Parallel GC, also known as the throughput collector, is a multi-threaded collector designed to optimize CPU utilization.

Characteristics:

• Uses multiple threads for minor and major garbage collection.
• Focuses on maximizing application throughput.
• Introduces stop-the-world pauses but processes garbage collection quickly.

Use Case:

• Best for applications that prioritize high throughput over low latency, such as batch processing systems.

How to enable it:

java -XX:+UseParallelGC -jar MyApp.jar

3. G1 (Garbage First) Garbage Collector

The G1 GC is designed for applications requiring predictable pause times while maintaining high performance.

Characteristics:

• Divides the heap into regions and prioritizes garbage collection based on the most occupied regions.
• Supports concurrent garbage collection to minimize pauses.
• Balances latency and throughput efficiently.

Use Case:

• Ideal for large-scale applications with stringent latency requirements, such as web services and real-time applications.

How to enable it:

java -XX:+UseG1GC -jar MyApp.jar

4. Z Garbage Collector (ZGC)

The ZGC is a scalable, low-latency garbage collector designed to handle terabytes of heap memory with minimal pause times.

Characteristics:

• Performs most of the garbage collection work concurrently.
• Keeps pause times below 10ms even with large heaps.
• Supports large-memory applications.

Use Case:

• Best suited for applications with massive memory footprints, such as cloud-native applications and big data processing.

How to enable it:

java -XX:+UseZGC -jar MyApp.jar

5. Shenandoah Garbage Collector

The Shenandoah GC aims to minimize pause times, similar to ZGC, but is designed for more general-purpose use.

Characteristics:

• Performs concurrent garbage collection to reduce pause times.
• Supports a wide range of workloads with efficient memory handling.
• Designed to work efficiently across different heap sizes.

Use Case:

• Suitable for applications requiring low-latency operations, such as interactive services.

How to enable it:

java -XX:+UseShenandoahGC -jar MyApp.jar

6. Epsilon Garbage Collector

The Epsilon GC is a special-purpose garbage collector that does nothing—it allocates memory but never reclaims it.

Characteristics:

• Does not perform actual garbage collection.
• Used for performance testing and memory allocation studies.
• Can lead to OutOfMemoryErrors when memory runs out.

Use Case:

• Best for benchmarking and debugging memory behavior.

How to enable it:

java -XX:+UseEpsilonGC -jar MyApp.jar

Choosing the Right Garbage Collector

Choosing the right garbage collector depends on the application’s needs, particularly its latency, throughput, and memory requirements.

Selection Criteria:

Garbage Collector	Best For	Latency	Throughput
Serial GC	Small applications	High	Low
Parallel GC	High-throughput apps	Medium	High
G1 GC	Balanced workloads	Low	High
ZGC	Large memory apps	Very Low	Medium
Shenandoah GC	Low-latency apps	Very Low	Medium
Epsilon GC	Testing purposes	N/A	N/A

General Recommendations:

• Use Serial GC for single-threaded applications or small embedded systems.
• Use Parallel GC for batch processing and applications needing high throughput.
• Use G1 GC for enterprise applications requiring a balance of performance and latency.
• Use ZGC for ultra-low-latency applications dealing with large heaps.
• Use Shenandoah GC for latency-sensitive interactive applications.
• Use Epsilon GC only for testing purposes.

Conclusion

Selecting the right garbage collector is critical for optimizing Java application performance. Different applications have varying memory management needs, and choosing the most suitable GC depends on factors such as memory footprint, response time requirements, and computational overhead.

For applications that demand low latency, ZGC and Shenandoah GC offer excellent solutions by reducing pause times to minimal levels. If raw processing power and throughput are the primary concerns, the Parallel GC is the best option. The G1 GC provides a balanced approach suitable for most enterprise applications, making it a common default choice. Meanwhile, the Serial GC remains a viable option for small-scale or embedded systems. Lastly, Epsilon GC, while not performing garbage collection, serves as a valuable tool for debugging and benchmarking.

Ultimately, the right garbage collector should be chosen based on profiling and real-world testing under production-like conditions. Developers should experiment with different GC algorithms, analyze application performance, and fine-tune JVM settings to achieve the best results. By making an informed choice, developers can significantly improve application responsiveness, scalability, and resource efficiency, ensuring smooth and reliable operation in diverse workloads.