Every Programming Language needs to efficiently manage Memory to create space for the smooth execution of new applications. In the Java programming language, such an operation is done with the help of the “Garbage Collection Algorithms in Java.”
Garbage Collection is highly needed to stop the Memory Leaks and optimize the performance of Java applications. In this article, we will discuss the Garbage Collection Algorithm and its different types along with its possible future.
So, let us start our discussion with the very basic definition of the Garbage Collection Algorithm in Java.
Summary Or Key Highlights:
- Garbage Collection is the process by which Java can remove programming wastes to make new spaces.
- The Java Garbage Collection Lifecycle is divided into 2 Generations.
- There are Six different types of Garbage Collection Algorithms in Java.
- Every Garbage Collection Algorithm in Java is different from each other by many perspectives.
- There are multiple reasons for which the Garbage Collection can trigger in any Java Program.
What Is The Garbage Collection (GC) In Java?
When we write any program in Java, there are some objects created in the memory that help to execute that program. When we frequently execute that application, those objects are stored in the memory. But, when we are not using them for a long time, those objects become waste.
In that case, the memory space will become occupied by such waste or garbage, and any new space to execute any new application will not be available. In that case, the Garbage Collection will be used.
Garbage Collection is the automatic process by which the older programming objects are removed from the memory space to make new spaces for new applications.
Historical Evolution Of Java Garbage Collection:
- 1990s: The Single Garbage Collector was introduced for single-threaded systems.
- 2000s: The Parallel Garbage Collector was introduced to increase performance.
- 2010s: The CMS and G1 Garbage Collection Algorithm started gaining popularity.
- 2020s: Some advanced Garbage Collection Algorithms like ZGC and Shenandoah GC were developed.
How Does Garbage Collection Work In Java? Read Below
After clearing the definition of the Garbage Collection in Java, we can now focus on its working process. The working process is divided into 4 Stages, from the creation to the dumping of the programming object.
Let us check the following diagram and the list where we have mentioned all the stages in a step-by-step format.
- Memory Allocation: The first stage is the Memory Allocation. Creating any Java Object with the “New” Keyword takes memory spaces in the Heap Memory.
- Object Life-Cycle: As long as the Java Application is in use, the created object will stay in the Memory Space where the object passes 3 Generations before becoming garbage.
- Converting Garbage: When we are not providing any Active Reference to the created object, the GC identifies the object as garbage and becomes eligible for collection.
- Garbage Collection: Any Garbage Collection Algorithm can be used and all of those wastes will be picked up and removed from the memory.
What Are Different Generations In Java Garbage Collection?
In the above section, we have seen that an object completes its Life Cycle in the memory as long as it is in use. During that period, the object passes 2 generations in the memory.
Let us check the following flowchart and the list where we have talked about those 2 Generations briefly.
- Young Generation: When the object is newly created and is in complete use, the object will fall into the Young Generation. The Young Generation can be further divided into 2 categories.
- Eden Space: The object that has not yet faced any GC Cycle will fall under this category.
- Survivor Space: The object that has faced a GC Cycle but has not yet been removed as it is in use will fall under the Survivor Space Category.
- Old Generation: When the object is not in use, it will fall under the Old Generation. When any object falls into the Old Generation, it will be treated as eligible for Garbage Collection.
What Are Different Types Of Garbage Collection Algorithms In Java?
We hope whatever we have discussed till now will be enough to clear your basic understanding of the Garbage Collection in Java. Now, it is time to move ahead into some more details.
Here, we will discuss 6 different types of GC Algorithms in Java. So, let us start with the very first one.
1. Serial Garbage Collector:
In this algorithm, a Single Thread is used by which we can do both Minor and Major Garbage Collection Tasks. During this algorithm, all other threads are paused, which makes it more efficient for small applications. The Serial Garbage Collector is a less Resource-intensive Algorithm.
Advantages:
- It is simple and has low overheads.
- The Serial approach will be best for small applications.
Disadvantages:
- This uses the Stop-the-World pauses to stop other threads.
- It is not applicable for large applications.
Application Field: We can use it in the Embedded Systems and Test Environments.
2. Parallel Garbage Collector (Throughput Collector):
The Parallel Garbage Collector or Throughput Collector uses multiple threads to do Garbage Collection for Minor Tasks. If we want to Maximize Application Throughput, then we should use this algorithm as it reduces the time spent on Garbage Collection.
Advantages:
- It reduces the pause time as it uses multiple threads.
- We can use it for the applications where Medium to Large heaps are present.
Disadvantages:
- It also uses the Stop-the-World pauses like the Serial Collector.
- It is not suitable for Latency-sensitive applications.
Application Field: We can use it for Server-side applications and applications with high CPU utilization.
3. Concurrent Mark-Sweep (CMS) Collector:
The CMS Collector does its work concurrently with other application threads and makes the application pause less. The CMS Collector follows a Multi-thread approach that decreases the Stop-the-World pauses. After the Java 9 Version, the use of the CMS Collector was highly reduced.
Advantages:
- The CMS Collector has a Low Pause Time.
- We can do the Concurrent Collection with the help of CMS Collector.
Disadvantages:
- When we use it, it requires High CPU Usage.
- We can face the Memory Fragmentation Issue with the CMS.
Application Field: We can use it for Financial Services and E-commerce Platforms where real-time transaction processing is done.
4. G1 (Garbage First) Garbage Collector:
Now, it is time for the G1 Garbage Collector. The G1 Garbage Collector first divides the Memory Heap into multiple divisions. Then, it works in a division first where most of the garbage is kept. That is the reason it is called the G1 (Garbage First). It uses both Parallel and Concurrent methods.
Advantages:
- With the G1 Collector, we can predict the Pause Time.
- We can easily handle the Large Heaps with the G1 Collector.
Disadvantages:
- If we use the G1 Collector for small heaps, we can face the Higher Overhead.
- G1 is not an easy garbage collection algorithm to work on.
Application Field: We can use it for Enterprise applications with large datasets.
5. Z Garbage Collector (ZGC):
After discussing the G1 garbage Collector, it is time for the 5th Garbage Collector Algorithm, which is the Z Garbage Collector. The Z Garbage Collector can be termed as one of the most efficient Garbage Collection Algorithms. The ZGC works on the Concurrent Approach,
Advantages:
- If we use ZGC, the Pause Time will remain under 10 milliseconds.
- We can handle large heaps from Gigabyte to large Terabyte.
Disadvantages:
- The ZGC is the new algorithm where we can see multiple updates.
- If we use ZGC, we can see the Higher Memory Overhead.
Application Field: We can use it in Real-time systems and Cloud-native applications.
6. Shenandoah Garbage Collector:
Last but not least, one will be the Shenandoah Garbage Collector Algorithm. If we want to perform Heavy-lifting Garbage Collection Operations, then the Shenandoah Garbage Collector algorithm will be needed. It is also a newly invented garbage Collection Algorithm.
Advantages:
- Here, the Pause Times are not dependable on the Heap size.
- We can do the Concurrent Collection with the help of Shenandoah Garbage Collector.
Disadvantages:
- The Shenandoah Garbage Collector consumes high CPU Resources.
- To work on the Shenandoah Garbage Collector, we should have Java 12 or a higher Version.
Application Field: We can use it for Microservices and Large-scale enterprise applications.
Comparison Table On Different Java Garbage Collection Algorithms:
Now, after discussing all the Garbage Collection Algorithms in Java, we can discuss their differences with the help of one Comparison Table.
In this section, we are going to make a comparison table on different GC Algorithms. Let us check the following comparison table to have a better understanding.
GC Names | Thread Type | Pause Time | Throughput | Memory Usage | Scalability | Best Use Cases |
Serial | Single | High | Medium | Low | Low | Small Applications |
Parallel | Multiple | Medium | High | Medium | Medium | High Throughput |
CMS | Multiple | Low | Medium | Medium | Limited | Low Latency |
G1 | Multiple | Low | High | Medium | High | Balanced Applications |
ZGC | Multiple | Very Low | Medium | High | Very High | Large Heaps |
Shenandoah | Multiple | Very Low | Medium | High | Very High | Real-Time Systems |
How To Ensure An Object Is Removed Using Garbage Collection In Java Program?
Now, in any Java Program, if we want to ensure that an object should be removed using Garbage Collection, then we can manually do that with the help of the GC() Method.
Let us check the following code where we have demonstrated it along with discussing the steps.
public class Main {
public static void main(String[] args) {
for (int i = 0; i < 1000; i++) // Allocating large Objects Using For Loop
{
String zap = new String(new char[10000]); // Creating Many Strings
}
System.out.println("Calling The Garbage Collection");
System.gc(); // Implementing The System GC (Garbage Collection)
System.out.println("Garbage Collection Is Done");
}
}
Steps Of The Program:
- At first, a For Loop will be executed, and a high value of String Object will be created.
- Then, we will call the GC() Function along with the “System” Method.
- This will remove every object created in the program manually.
Output:
What Are Some Common Tuning Guidelines For Java Garbage Collection Algorithms?
After discussing all the GC Algorithms, it is time for a Common Tuning Guideline. The Tuning Guideline is necessary in Java Virtual Machine to improve application performance and optimize memory use as well. We can do tuning when our application is facing slow performance or long GC pauses.
Let us check the below list where some Common Tuning Guidelines for all the GC Algorithms are mentioned.
java -Xms1g -Xmx4g \
-XX:ParallelGCThreads=8 \
-XX:MaxGCPauseMillis=200 \
-Xlog:gc* \
-jar myApp.jar
- We have to set the Heap Size properly. For that, we can use the JVM Options like -Xms (Initial) and -Xmx (Maximum).
- Using the JVM Option -XX: ParallelGCThreads we can adjust the Garbage Collection Threads based on available CPU Cores.
- To Control Pause Time, we can use the JVM Option -XX: MaxGCPauseMillis which helps to balance latency and throughput.
- If we want to monitor & analyze GC Logs, we can use the JVM Option -Xlog:gc* which enables logging.
A Case Study On Practical Use Of Java Garbage Collection:
In this section, we will take a case study and let you know how the Java Garbage Collection is implemented in the Practical Field to optimize the Java Application Performance.
Let us start with the following scenario:
Suppose a Fintech Company that has a Real-time Trading Platform facing performance issues during peak trading hours. As the platform uses High Transaction Volumes, the user experience is getting hampered by the unpredictable GC Pauses.
The Application was initially using the CMS Collector Algorithm with the Heap Size as -Xms4G and -Xmx8G. How do we optimize this to overcome the challenge?
Optimization Strategy:
At first, from the CMS Collector, we have to switch to the G1 Garbage Collector Algorithm and make the following configurations:
-XX:+UseG1GC
-Xms8G -Xmx8G
-XX:MaxGCPauseMillis=200
-XX:G1HeapRegionSize=16M
-XX:InitiatingHeapOccupancyPercent=45
- At first, the Heap Size will not be changed. Whatever was for CMS, the same will be for G1.
- Later, the Pause Time Goal will be set at 200 milliseconds to balance the performance.
- Now, the Heap Region Size is set to 16 MB, which will decrease the Compaction Time.
- Later, the Heap Occupancy will be set to 45% which will avoid the Large Memory Sweeps.
Before And After Performance Metrics:
Metric | Before (CMS GC) | After (G1 GC) | Improvements |
Average GC Pause | 500ms – 2s | 100ms – 250ms | 75% Deduction |
Throughput | 85 % | 95% | 10% Increase |
Latency Type | Frequent | Minimal | Stable |
Memory Usage | 7 GB | 6.5 GB | More Efficient |
What Factors Trigger Any Garbage Collection Algorithm In Java?
If you are thinking that the Garbage Collection Algorithm can be triggered at any time and you might lose some critical objects, then you are thinking wrong. To trigger any GC Algorithm, there should be some factors behind it.
Let us have a look at the following list where some important factors are mentioned that can trigger Garbage Collection in Java.
- When the Memory Allocation fails for any new application, the JVM can trigger the GC Process.
- Developers can manually call the GC Process using the System.GC() Method.
- If the Heap Space Threshold value is exceeded, then the JVM can trigger GC to avoid exceptions.
- If the Old Generation Space of the heap is fully occupied, then the GC will remove spaces from there.
- In the Eden Space as well, if there is no space for the new application, the GC can work there.
What Will Be Some Future Trends In Java Garbage Collection?
As we are approaching the end of the discussion, it will be the right time to disclose the Future Trends of the Garbage Collection Algorithms. This will help us to know which GC Algorithm will become more efficient and more demanding in the future.
Let us check the following list from where we will understand the future of the GC Algorithms in Java.
- We can assume that the ZGC and Shenandoah Algorithms will become more efficient in achieving the Near-zero Pause Time.
- We predict that all GC Algorithms will become more effective in handling large heaps in Cloud-native Applications.
- The GC Algorithms will become more advanced and the Self-tuning Capabilities will present to reduce the Manual Configuration workload.
- The GC Algorithms will become more optimized to provide better results in Kubernetes and Docker environments.
- The GC Algorithms will perform better in Real-time Systems like Gaming, Financial Trading, High-frequency Transaction Systems, etc.
How To Choose The Right Java Garbage Collection Algorithm?
In this article, we have seen different types of Garbage Collection Algorithms in Java. Now, before we conclude our discussion, we would like to shed some light on the tips that we can use to pick up the right GC Algorithm for any Java Application.
Let us have a look at the following list to know more about those important tips.
- Based on the application type, we need to select between the Serial, G1 Collector, and ZGC.
- If there is any Large Heap we can use the G1, ZGC and for Small Heaps we can use the Serial Collector.
- We have to choose the low-latency collectors (G1, ZGC) for real-time systems.
- The high-throughput collectors (Parallel GC) can be used for batch processing.
- If we are working on the Multi-Core System, then the Parallel GC will be the best one.
Conclusion:
In the end, we can say it is very important to know about the “Garbage Collection Algorithms in Java”.
However, we will advise you to clear the basics of Java programming before moving to such a complex and advanced topic in Java. If your basics in Java are not clear, you will not even understand the beginning of the Java GC Algorithms.
Takeaways:
- Java Garbage Collection removes wastes from the memory in four effective steps.
- We will find the Young and Old Generations in the Java Memory Heap Spaces for the objects.
- Serial, Parallel, CMS, G1, ZGC, and Shenandoah are some important Garbage Collector Algorithms.
- We can do the Garbage Collection Manually using the System.GC() Method in Java Programming.
- To optimize any Java Application Performance, we have to use the JVM Options for different GCs.
