Serial GC Tuning
Published: 2023-11-27 07:37:33


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Tailored for simplicity and effectiveness, the Serial GC operates with a single-threaded approach, making it particularly relevant for smaller-scale applications and scenarios where stringent latency requirements aren’t the primary concern. In this post, we will explore techniques to tune Serial GC for enhanced performance specifically. However, if you want to learn more basics, you may watch this [Garbage Collection tuning talk](https://www.youtube.com/watch?v=6G0E4O5yxks) delivered in the JAX London conference.

**How to enable Serial GC?**
You can enable the Serial Garbage Collector in your Java application by adding the following JVM argument when launching your application:

-XX:+UseSerialGC

**When to use Serial GC?**
You can consider using Serial GC in the following scenarios:

a. Smaller-Scale Applications: Serial GC’s simplicity and single-threaded nature make it a good fit for smaller-scale applications. In these scenarios, the overhead of managing multiple threads for garbage collection may outweigh the benefits.

b. Resource-Limited Environments: In environments with limited resources, such as embedded systems or environments with constrained memory, the Serial GC’s lightweight approach can be advantageous.

c. Desktop Applications: For desktop applications with moderate memory requirements and where simplicity is preferred, the Serial GC can be a suitable choice. It ensures effective garbage collection without the added complexity of multi-threading.

d. Development and Testing: During development and testing phases, when quick feedback and simplicity are essential, using the Serial GC can help identify and address issues without the complexity introduced by more sophisticated collectors.

e. Educational Purposes: For educational or training purposes, using the Serial GC provides a clear and understandable introduction to garbage collection concepts without the added complexity of parallel or concurrent collectors.

**Serial GC tuning parameters**
In this section let’s review important Serial GC tuning parameters that you can configure to your application.

**1. -Xms and -Xmx**
-Xms sets the initial heap size when the Java Virtual Machine (JVM) starts, and -Xmx sets the maximum heap size that the JVM can use. Setting both values to be the same value, ensures a fixed and non-resizable heap size. This configuration reduces hiccups associated with heap management, providing stability and predictable memory usage for your application. You may refer to this article to learn the detailed benefits of setting initial and maximum heap size to the same value.

**2. -XX:MaxGCPauseMillis**
To control the maximum desired pause time for garbage collection, the -XX:MaxGCPauseMillis=<time> flag comes into play. This parameter allows you to balance the trade-off between responsiveness and overall throughput by specifying the acceptable pause time.

**3. -XX:GCTimeRatio**
Adjusting the ratio of time spent in garbage collection compared to application time is facilitated by the -XX:GCTimeRatio=<n> flag. For example, if you set -XX:GCTimeRatio=4, it means that the JVM will aim to spend 1/4th of the total time on garbage collection and allocate the remaining 3/4th for application processing. Lower values of GCTimeRatio prioritize the application’s responsiveness, as less time is dedicated to garbage collection, potentially resulting in shorter pause times. On the other hand, higher values prioritize garbage collection throughput, which may lead to longer pauses but more efficient use of available CPU resources.

**4. -XX:MaxTenuringThreshold**
For objects in the young generation, the tenuring threshold defines when an object is promoted to the old generation. You can set the maximum tenuring threshold using the -XX:MaxTenuringThreshold=<n> flag, influencing the garbage collection strategy.

**5. -XX:+UseAdaptiveSizePolicy**
For dynamic adjustment of heap sizes, the -XX:+UseAdaptiveSizePolicy flag enables adaptive sizing policies for the Serial GC. This feature allows the JVM to dynamically adjust the size of the young and old generations based on the application’s memory requirements.

**Studying Serial GC behavior**
Studying the performance characteristics of Serial GC is best [achieved by analyzing the GC log](https://blog.gceasy.io/2022/02/07/how-to-do-gc-log-analysis/). The GC log contains detailed information about garbage collection events, memory usage, and other relevant metrics. There are several tools available that can assist in analyzing the GC log, such as [GCeasy](https://gceasy.io/), [IBM GC & Memory visualizer](https://developer.ibm.com/javasdk/tools/), [HP Jmeter](https://myenterpriselicense.hpe.com/cwp-ui/free-software/HPJMETERSW), [Google Garbage cat](https://github.com/mgm3746/garbagecat). By using these tools, you can visualize memory allocation patterns, identify potential bottlenecks, and assess the efficiency of garbage collection. This allows for informed decision-making when fine-tuning Serial GC for optimal performance. 

**Conclusion**
We hope this post gave a good overview on Serial GC tuning parameters. By adjusting key parameters like heap size, thread management, and utilizing tools such as GCeasy and IBM GC & Memory visualizer to analyze GC logs, developers can tailor the Serial GC to meet the specific needs of their applications.