Java is often considered a superior programming language choice owing to its high portability, strong memory safety, and rapid development cycle. However, this superiority comes with increased complexity within Java software stacks, driven by the extensive use of layered libraries, rising levels of abstraction, and the combination of interpretation and just-in-time compilation. This complexity disjoins source code and its execution details on the underlying hardware, making it challenging to write efficient Java code. Performance tracing is key to bridging this gap by providing detailed, temporally ordered insights into a program's runtime behavior. Existing tracing approaches generally fall into two categories: (1) instrumentation, which enjoys high accuracy but incurs significant overhead, and (2) sampling, which enjoys low overhead but sacrifices accuracy.

We introduce TRACE4J, a novel performance tracing tool for Java that overcomes the limitations of existing approaches. TRACE4J intelligently integrates CPU hardware facilities (performance monitoring units and breakpoints), the JVM tool interface, the Linux perf_event interface, and instruction decoding to deliver lightweight, flexible, and insightful performance tracing. It applies to unmodified Java programs, runs on standard JVMs and commodity CPUs, and provides both end-to-end and on-demand tracing, making it suitable for production environments. Through evaluation, we demonstrate TRACE4J’s ability to deliver actionable performance insights with low overhead (no more than 5% time and memory impact). Using these insights, we were able to optimize several Java benchmarks and real-world applications, achieving substantial performance gains.