Introduction

IBM Semeru Runtime is an OpenJDK distribution designed to run any Java application — be it for traditional enterprise workloads, cloud-native environments, or microservices. Semeru ensures compatibility with all Java workloads, providing the same reliability as other popular distributions like Oracle JDK or OpenJDK. What sets Semeru apart is its performance optimizations, including faster startup times, lower memory usage, enhanced garbage collection (GC), and more efficient JIT compilation.

In this blog, we’ll explore the key features of IBM Semeru Runtime, from faster application startup to improved memory management, and discuss how these features can help developers optimize Java applications in any environment.

Getting Started with IBM Semeru

If you’d like to try IBM Semeru locally, the easiest way is through SDKMAN! — a popular tool for managing Java versions.

Install IBM Semeru JDK 21 using the following commands:

# Install SDKMAN
curl -s "https://get.sdkman.io" | bash
source "$HOME/.sdkman/bin/sdkman-init.sh"

# Install Semeru JDK 21
sdk install java 21.0.6-sem

# Verify the installation
java -version

Now you’re ready to start building and running Java applications using IBM Semeru — before containerizing or deploying them in the cloud.

Key Features of IBM Semeru Runtime

IBM Semeru Runtime comes with several powerful features designed to maximize the performance and efficiency of Java applications. These features help optimize memory usage, improve application responsiveness, and reduce overhead in various types of workloads.

1. Faster Startup Times

In modern Java applications, particularly those running in containerized or cloud environments, startup times can have a significant impact on overall performance, especially in scaling scenarios. IBM Semeru is designed to reduce startup times, allowing Java applications to initialize quickly and stay responsive when scaling up or down.

• Benefit: Ideal for applications that need to quickly start and scale based on demand, such as microservices and serverless environments.

2. Lower Memory Usage

Efficient memory management is crucial for Java applications, especially in environments where resources are limited or when running in containers. IBM Semeru uses advanced memory optimizations, ensuring that Java applications consume less memory while maintaining high performance.

• Benefit: Reduces memory consumption, allowing you to run more applications on the same infrastructure and scale efficiently.

3. Optimized Garbage Collection (GC)

Garbage collection (GC) plays a key role in JVM performance. Poorly optimized GC can cause application pauses and degrade performance. IBM Semeru has GenCon GC, which is designed to minimize pause times and improve overall GC efficiency. This results in faster and more responsive applications.

• Benefit: Helps keep your applications responsive by reducing GC pauses, particularly important for real-time applications and high-traffic systems.

4. JIT Optimization Features

Just-In-Time (JIT) compilation is another critical factor for performance. IBM Semeru optimizes JIT compilation to improve the runtime performance of Java applications. By using Eclipse OpenJ9’s adaptive compilation techniques, Semeru dynamically tunes application performance based on workload characteristics, ensuring that your application runs efficiently.

• Benefit: Improves runtime performance, making applications more responsive and reducing the overhead associated with long-running processes.

5. Cloud-Native Optimizations

IBM Semeru is optimized for running in cloud-native environments. It integrates seamlessly with Kubernetes and Docker, enabling developers to efficiently deploy and manage Java applications in containers. Features such as automatic memory sizing and Kubernetes resource optimization help applications scale dynamically to meet varying demands.

• Benefit: Makes it easier to deploy Java applications in cloud environments, with optimizations that allow for better scalability and resource management.

6. Semeru’s Shared Class Cache (SCC)

IBM Semeru includes a Shared Class Cache (SCC), which stores frequently used Java class metadata in memory. This reduces the need to reload classes from disk on every run, improves class loading efficiency, and lowers overall execution overhead.

Benefit: Reduces class loading overhead.

Note: To ensure consistent performance benefits in containerized environments, it’s recommended to create the cache during the container image build process. Creating the cache at runtime may result in it not persisting across container runs, thereby limiting its effectiveness.

Best Practices for Optimizing Java Applications with Semeru

To get the most out of IBM Semeru, developers can follow these best practices to further optimize application performance:

1. Set Memory for Containers

In cloud environments, especially when using containers, it is important to adjust memory settings for optimal performance. Semeru allows you to dynamically adjust memory usage, helping to prevent memory bottlenecks and optimize performance in containers.

Command:

java -XX:MaxRAMPercentage=75 -Xms256m -Xmx512m -jar myapp.jar

• Benefit: Optimizes memory usage for containerized applications, ensuring efficient resource allocation.

2. Use GenCon GC for Low-Latency Applications

For applications that require low latency, such as real-time services, using GenCon GC is highly recommended. This garbage collector minimizes pause times, allowing the application to stay fast and responsive even under heavy load.

Command:

java -Xgcpolicy:gencon -jar myapp.jar

• Benefit: Keeps your application responsive by reducing pauses during garbage collection.

3. Enable Shared Class Cache (SCC)

To minimize the overhead of class loading, Semeru’s Shared Class Cache (SCC) stores frequently used Java class metadata in memory. This improves class loading efficiency and reduces overall execution overhead

Command:

java -Xshareclasses:name=myCache,nonFatal -jar myapp.jar

• Benefit: Minimizes the overhead of loading classes.

4. Set Kubernetes Resource Requests and Limits

If you are running Java applications on Kubernetes, it’s important to set appropriate resource requests and limits to optimize performance. Semeru works well with Kubernetes, allowing you to define these settings to ensure your application has the resources it needs to run efficiently.

Example YAML:

resources:
  requests:
    memory: "512Mi"
    cpu: "0.5"
  limits:
    memory: "1024Mi"
    cpu: "1"

• Benefit: Ensures that the application has enough resources while preventing overuse of memory and CPU, maintaining stable performance.

Conclusion

IBM Semeru Runtime offers a wide range of performance-enhancing features that help Java applications run faster, use memory more efficiently, and stay responsive under load. Whether you’re deploying traditional Java applications, microservices, or containers, Semeru is designed to deliver optimized performance across various environments.

Key Benefits:

• Faster startup times, reducing application initialization delays.
• Lower memory usage, allowing you to scale more applications without additional infrastructure costs.
• Optimized garbage collection for improved responsiveness.
• JIT optimizations that enhance runtime performance.
• Cloud-native optimizations for scalable deployments in Kubernetes and Docker.

By adopting IBM Semeru, developers can ensure that their Java applications perform efficiently, scale effectively, and are well-equipped for future demands.