Advanced Java Garbage Collection — G1 and ZGC
Advanced Java Garbage Collection — G1 and ZGC
Hello everyone! In this article, we discuss advanced Java Garbage Collection: G1 and ZGC.
Introduction
Both garbage collectors are designed to optimize memory management in large-scale applications by improving the efficiency of memory allocation, deallocation, and garbage collection. Both G1 and ZGC are designed to reduce pauses while performing the garbage collection cycle and improve overall system performance.
G1 or Garbage First
G1 is a fully incremental garbage collector that divides memory into multiple regions. The G1 garbage collector is concurrent. The division approach brings more efficient usage of memory by dynamically allocating objects in different regions based on their usage patterns.
The key features:
1. Region-based Heap
- The heap is divided into several large regions
- Each region can be managed independently
2. Concurrent collection
- Garbage collection occurs concurrently with application execution, minimizing pauses.
- The G1 utilizes a parallel collector to perform the actual work of collecting garbage
3. Incremental collection
- By using incremental collection techniques that allow parts of the heap to be collected without stopping the entire application
4. Live Data Set Tracking
- “Young set” and “old set” are used to track live objects
- The old set handles major collections, while the young set is used for minor collections
5. Scavenger Mechanism
- In a situation when the young set becomes full, G1 uses the scavenger to reclaim memory by moving live objects from young to an old set
- This process helps in reducing fragmentation and improving memory utilization.
ZGC (Z Garbage Collector)
ZGC is a garbage collector designed for a modern multi-core system with a low latency in mind. It is designed to provide excellent performance with minimal pauses, making it reasonable for applications that require high responsiveness and throughput.
Key features:
1. Concurrent Mark-Sweep
- ZGC employs a concurrent mark-sweep algorithm that enables the application to continue running during garbage collection
- Reduced impact on system performance
2. Incremental collection
- The same as G1
3. Memory management
- ZGC manages memory allocation and deallocation efficiently to minimize fragmentation
- To reduce fragmentation ZGC uses a compacting collector that can reclaim memory by moving live objects to a contiguous block
4. Lager Heap Support
- With ZGC you do not need an extensive amount of swap space, since it is designed to handle large heaps with millions of allocated objects.
How to enable G1 or ZGC
You can enable ZGC through system properties:
G1
System.setProperty("java.lang.management.GarbageCollectorDebugOutput", "true");
System.setProperty("sun.java.command", "-XX:+UseG1GC -XX:MaxGCPauseMillis=<desired_max_pauses>ms");or ZGC (Available from Java 17 onward)
System.setProperty(“java.lang.management.GarbageCollectorDebugOutput”, “true”);
System.setProperty(“sun.java.command”, “-XX:+UseZGC -XX:GCPauseTimeBudget=<budget_in_ms>”);Conclusion
G1 and ZGC are modern garbage collectors that offer noteworthy improvements in memory management for Java applications. By using it developer can enhance the performance of their applications. Knowledge about the underlying principles of these garbage collectors can help you decide what to choose
References
If you are interested in more information about garbage collectors please refer to the official documentation available at Oracle Java Documentation
For ZGC configuration details, visit the ZGC documentation