Understanding Tiered Compilation in OpenJDK

2023/08/22

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The article explains how tiered compilation works in the OpenJDK HotSpot runtime system, which is responsible for optimizing the execution of Java programs. The system consists of multiple compilers, an interpreter, and various garbage collectors. Tiered compilation is a mechanism that selects the most suitable compiler for each method based on its execution frequency. The idea behind tiered compilation is that a small portion of the code consumes most of the execution time, so using a simpler compiler for less frequently executed methods and an optimizing compiler for frequently executed methods can improve performance. The article provides a hypothetical example to illustrate the concept, comparing the compilation and execution costs of different compilers. By employing tiered compilation, the OpenJDK HotSpot runtime system aims to generate efficient machine code while minimizing runtime cost. This optimization technique is relevant for developers working with Java as it helps them understand how the Java runtime optimizes their code.