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Java / GraalVM Interview questions

Why is heap size configuration different for native image versus a JVM?

A standard JVM defaults its heap sizing based on available system memory and lets you tune it with familiar flags like -Xmx and -Xms at launch, with HotSpot's ergonomics adjusting things like young-generation size dynamically.

A native image executable embeds its own garbage collector (Serial GC by default in Community Edition, with G1 available on Oracle GraalVM), and while it accepts similar-looking runtime flags (-Xmx, -Xmn) at launch time, some GC-related tuning must instead be baked in at build time via -R: flags, because the GC implementation itself is selected and partly configured when the executable is compiled, not when it's run.

native-image -R:MaxHeapSize=256m -jar app.jar
./app -Xmx256m

In practice this means teams need to think about two separate configuration surfaces - build-time GC selection/limits and run-time heap flags - rather than the single unified runtime flag set they're used to on a normal JVM.

Why can't all heap tuning for a native image be done purely at launch time?
Which GC is the Community Edition default for native images?

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What is GraalVM? What are the main components of GraalVM? What is Native Image in GraalVM? What is the Graal compiler? What is the purpose of Substrate VM? What are the editions of GraalVM? How do you install GraalVM using SDKMAN? How do you apply the gu utility to manage components? Define polyglot programming in the context of GraalVM? Describe the Truffle language implementation framework? List the languages GraalVM can run? What is ahead-of-time (AOT) compilation? What are the benefits of using GraalVM Native Image? What is a fallback image? Describe reflection configuration in native image? What is class initialization at build time? How do you set GraalVM as your default JDK? How do you generate a native executable with native-image? What is the purpose of the Graal compiler's tiered execution? Define the Graal compiler's JIT role within HotSpot? What are the types of GraalVM components installable via gu? Describe the polyglot Context API? What is the purpose of Truffle's Partial Evaluation? Explain the purpose of resource-config.json in native image? What is the purpose of the reachability metadata repository? Why is GraalVM's JIT compiler often faster than the default HotSpot C2 compiler? What is the difference between GraalVM Community and Enterprise editions? When should you choose Native Image over running on the JVM? How does the native-image build process work end-to-end? Why doesn't Native Image support dynamic class loading by default? How do you troubleshoot "ClassNotFoundException" in a native image at runtime? What is the difference between build-time and run-time class initialization? How can you optimize native image build time for large applications? Why should you use Profile-Guided Optimization (PGO) with Native Image? How does escape analysis work in the Graal compiler? Explain the execution flow of a polyglot call between Java and JavaScript on GraalVM? What happens when you use Java dynamic proxies with Native Image? Why is heap size configuration different for native image versus a JVM? How do you troubleshoot missing reflection metadata errors during native image build? Explain the internal working of Truffle's AST specialization? Difference between Espresso and running native Java bytecode on the JVM? Why doesn't Native Image support arbitrary bytecode generation at runtime? How can you optimize the memory footprint of a native image executable? Explain the lifecycle of a Truffle language implementation from parsing to execution? Difference between GraalVM Native Image and traditional Docker-based JVM deployment for startup time? How does GraalVM's deoptimization mechanism work when a speculative optimization fails? When would you choose GraalVM Enterprise's G1 GC support over Community's Serial GC for native image? How do you debug a native image application when standard Java debuggers don't attach? Explain the internal working of the Graal compiler's speculative optimizations? Why is GraalVM particularly well suited for serverless and microservices workloads?
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