Exploring GraalVM: How to Speed Up Java Applications and Reduce Memory Footprint

GraalVM is an advanced JIT (Just-In-Time) compiler and execution environment designed to optimize JVM-based languages like Java, Scala, and Kotlin, as well as other languages like JavaScript, Python, and Ruby.

The standout feature of GraalVM is its Native Image capability, which enables you to compile Java applications into native executables. This drastically improves startup times and reduces the memory footprint of your applications—perfect for microservices and cloud-native environments.

GraalVM offers two main ways to improve the performance of your Java applications:

1/ Graal JIT Compiler: The JIT compiler is optimized for peak performance, making it a direct replacement for the default HotSpot JVM compiler. The Graal JIT dynamically compiles Java bytecode during runtime, allowing applications to execute faster as Graal applies advanced optimizations.

2/ Native Image: This is where things get exciting. GraalVM’s Native Image utility compiles your Java application ahead of time (AOT) into a native executable. This drastically reduces memory usage and startup time, which is crucial in microservices environments where apps need to start up fast and use as little memory as possible.

How GraalVM Works Under the Hood

• The Graal JIT Compiler

• GraalVM’s JIT compiler is designed to take full advantage of modern CPU architectures. It performs aggressive optimizations by:

• Inlining methods: Graal inlines heavily used methods, reducing the overhead of method calls.

• Eliminating unused code paths: Unnecessary code is trimmed during compilation, further improving execution speed.

• Speculative optimizations: Graal speculatively optimizes code based on runtime profiling, leading to enhanced performance for hot code paths.

Native Image Compilation
When you use GraalVM to compile a Java application into a native executable, it performs a process called SubstrateVM, which analyzes and includes only the necessary parts of the Java runtime. This results in:

• Significantly faster startup times: Native images bypass the JVM, so there’s no need to wait for JIT compilation or classloading during startup.

• Lower memory consumption: Native images reduce the memory footprint because the overhead from the JVM is eliminated.

Practical Example: Microservices with GraalVM
Let’s imagine you’re building a microservice-based architecture.

Here’s how GraalVM can help:

Startup Time: In a traditional JVM environment, microservices need time to warm up as the JIT compiler optimizes bytecode. With GraalVM’s Native Image, microservices can start almost instantly, making them ideal for auto-scaling and serverless scenarios.

Memory Efficiency: Running multiple microservices can bloat memory usage. Native Images drastically reduce the amount of memory consumed per service, which is especially beneficial in containerized environments like Kubernetes.

Deployment Size: GraalVM strips out unnecessary Java classes and resources, resulting in smaller application binaries. This reduces the disk space required to store containers and improves the speed of deployments.

Using GraalVM to Compile a Native Image
Here’s a simple example of how you can create a native image for a basic Java application:

First, install GraalVM (make sure to grab the version for your operating system).

Add the native-image component using gu (GraalVM Updater):

Compile a simple Java class into a native executable:

Compile the Java file using native-image:

Run the resulting executable:

You’ll notice the application starts immediately, and the memory usage is far lower than what you’d expect with a regular JVM-based app.

Performance Implications of GraalVM

• Reduced Latency: Native images execute instantly compared to JVM-based apps, which have to go through initialization phases.

• Lower Memory Usage: By avoiding the JVM’s garbage collector and other overhead, native images consume significantly less memory.

• Deployment Speed: Native executables are smaller and more efficient to deploy, making them ideal for cloud-based microservices.

However, it's important to note that native images may not achieve the same peak runtime performance as a well-optimized JVM JIT-compiled application. For long-running applications, you might still benefit more from the Graal JIT compiler over Native Image.