Garbage collection in Java applications

At Arteco Consulting SL, we are experts in custom development consulting and understand how memory is managed in Java through garbage collection (GC). In this article, we will share what we have learned to ensure our systems are configured for optimal Java performance.

The Vital Role of Garbage Collection in Java Memory Management

Garbage collection (GC) plays a fundamental role in memory management in Java. Its primary function is to reclaim memory that is no longer in use. To carry out this task, garbage collection utilizes its own set of threads, known as GC threads. However, sometimes the Java Virtual Machine (JVM) may end up with too many or too few GC threads.

How to Determine the Number of GC Threads in Your Application?

It is possible to discover the number of GC threads in your application by analyzing a thread dump. This process involves capturing a thread dump from the production server and analyzing it with a thread dump analysis tool. The tool will immediately report the GC thread count, as shown in Figure 1.

You can manually adjust the number of GC threads by setting the following two JVM arguments:

• -XX:ParallelGCThreads=n: Sets the number of threads used in the parallel phase of the garbage collectors
• -XX:ConcGCThreads=n: Controls the number of threads used in the concurrent phases of the garbage collectors

What is the Default GC Thread Count?

If you do not explicitly set the GC thread count using the two previous JVM arguments, then the default GC thread count is derived based on the number of CPUs in the server or container.

Can the JVM End Up with Too Many GC Threads?

It is possible for the JVM to have too many GC threads without you realizing it. This typically occurs because the default number of GC threads is automatically decided based on the number of CPUs in your server or container.

When there are too many GC threads, the JVM consumes more resources than necessary since all these threads are competing for the same CPU resources. This is particularly problematic in containerized environments, where multiple applications share the same CPU cores.

Why Can Having Too Many GC Threads Be a Problem?

There are several reasons why having too many GC threads can be detrimental to your Java application's performance:

• Increased context switching
• Waste of CPU resources
• Memory contention
• Increased GC pause times and decreased performance
• Higher latency
• Diminishing returns

Why Can Having Too Few GC Threads Be a Problem?

However, having too few GC threads can also be problematic:

• Increased garbage collection time
• Increased application latency
• Reduced efficiency
• Inefficient CPU utilization
• Increased risk of memory errors and memory leaks

Solutions to Optimize GC Thread Count

If your application suffers from performance issues due to an excessive or insufficient number of GC threads, you may consider manually adjusting the GC thread count using the previously mentioned JVM arguments:

-XX:ParallelGCThreads=n -XX:ConcGCThreads=n

However, before making these changes in production, it is vital to observe your application's behavior. Start by collecting and analyzing GC logs using appropriate tools.

Conclusion

Balancing the number of GC threads is essential to ensure that your Java application runs smoothly. By carefully monitoring and adjusting these configurations, you can avoid potential performance issues and keep your application running efficiently.

At Arteco Consulting SL, we take pride in our commitment to providing our clients with custom software solutions that enhance the efficiency and productivity of their operations. In combination with our in-depth knowledge of Java performance tuning best practices, we offer our clients a competitive edge. If you have any questions about how we can help you improve the performance of your Java application, please do not hesitate to contact us.