types of garbage collection in java

Tommy 93 Published: 08/17/2024

types of garbage collection in java

I'll respond in English this time!

Java provides several types of garbage collection mechanisms to automatically manage memory and remove unnecessary objects from the heap, known as garbage. Here are some common types of garbage collectors used in Java:

Mark-and-Sweep (M&S): This is the most commonly used garbage collector in Java. It works by first marking all reachable objects (i.e., those that can be accessed by live threads) and then sweeping the heap to remove unmarked objects.

M&S algorithm consists of two phases:

Mark phase: During this phase, the garbage collector iterates through the heap, starting from a set of roots (such as the stack and global variables), and marks all reachable objects. Sweep phase: Once marking is complete, the garbage collector iterates through the heap again, freeing any unmarked objects (i.e., those that were not reached during the mark phase). Concurrent Mark-and-Sweep (CMS): This is an alternative to M&S and is designed for low-pause-time applications. CMS uses multiple threads to perform concurrent marking and sweeping, which reduces pause times compared to traditional M&S. Garbage-First (G1) Garbage Collector: Introduced in Java 7, G1 is a newer garbage collector that aims to reduce pause times even further than CMS. G1 divides the heap into smaller regions called "humongous" and then collects garbage concurrently with the application. Incremental Concurrent Mark-and-Sweep (Iv-CMS): This is an enhancement to CMS, which performs incremental marking and sweeping in parallel with the application's execution. Iv-CMS can reduce pause times even further than traditional CMS. ZGC: The Z Garbage Collector, introduced in Java 11, is a low-pause-time garbage collector designed for real-time applications that require predictable garbage collection pause times. ZGC uses a generational approach to divide the heap into three regions: young, old, and humongous. Serial Garbage Collector: This is the simplest form of garbage collector, which runs in a single thread and does not use multiple threads for marking and sweeping. The serial garbage collector is suitable for small applications that do not require concurrent garbage collection. Generational Garbage Collection: Java uses a generational approach to divide objects into three generations based on their age: Young generation (also known as the Eden space): Newly created objects are stored here. Old generation: Objects that survive a certain number of garbage collections are promoted to this generation. Tenured generation: The old and tenured generations are combined to form the tenured generation, which is collected less frequently than the young generation.

Java's garbage collectors can be tuned using various options, such as the -Xincgc flag for incremental concurrent marking or the -XX:ConcGCThreads flag to set the number of concurrent GC threads. The choice of garbage collector and tuning parameters depends on the specific requirements of your application, such as pause time, memory usage, and concurrency needs.

Java garbage collection tutorial

I apologize for the language restriction earlier! Here's a comprehensive tutorial on Java Garbage Collection in over 300 words:

What is Garbage Collection?

In object-oriented programming, memory management is crucial to ensure that your program runs efficiently and doesn't consume too much system resources. Java, being an object-oriented language, uses a concept called Garbage Collection (GC) to automatically manage the memory allocated for objects.

How does Garbage Collection work?

When you create an object in Java, it occupies a portion of memory. As your program runs, you may no longer need or reference these objects. In such cases, the memory occupied by those objects becomes "garbage." The JVM (Java Virtual Machine) periodically identifies and reclaims this garbage memory using Garbage Collection.

Garbage Collection Process:

The GC process involves two main steps:

Marking: During this step, the GC algorithm walks through all the objects in your program's heap space and marks as "live" or "reachable" those objects that are referenced by other live objects (e.g., variables, arrays, or data structures). Sweeping: After marking, the GC algorithm sweeps the heap space, identifying any remaining objects (i.e., not marked as "live") as garbage. The JVM then reclaims this memory to free up resources for future allocations.

Types of Garbage Collection:

Java provides two primary garbage collection algorithms:

Mark-and-Sweep Algorithm: This is the default algorithm used by the Java HotSpot VM (JVM). It's a generational algorithm, which means it divides the heap space into generations based on object lifespan. Concurrent Mark-and-Sweep Algorithm: This algorithm is similar to the mark-and-sweep algorithm but runs concurrently with the application's execution. This helps reduce pause times and improves overall system responsiveness.

Garbage Collection Tuning:

To optimize garbage collection performance, you can tune various JVM parameters, such as:

-Xmx (Maximum heap size): Set a suitable value for your program's memory requirements. -XX:+UseConcMarkAndSweepGC: Enable concurrent mark-and-sweep algorithm to reduce pause times. -XX:NewSize and -XX:MaxNewSize: Control the sizes of young generations (e.g., Eden space).

Best Practices for Garbage Collection:

To ensure efficient garbage collection:

Minimize Object Creation: Reduce the frequency of object creation to reduce garbage generation. Use Weak References: Use weak references or soft references to facilitate garbage collection when objects are no longer needed. Profile Your Program: Analyze your program's memory usage using profiling tools to identify performance bottlenecks.

Conclusion:

Java Garbage Collection is an essential mechanism for managing object-oriented programming in Java. Understanding how it works and tuning its parameters can help you optimize your program's performance, reduce pause times, and ensure efficient memory management.

References:

Oracle JVM Documentation (https://docs.oracle.com/en/java/javase/11/docs/spec/jvms/) Java Tutorials: Memory Management and Garbage Collection (https://docs.oracle.com/javase/tutorial/essential/java/gc.html) Java Performance Tuning with Garbage Collection (https://www.baeldung.com/java-performance-tuning-garbage-collection)