One Method Was Using 71% of CPU. Here's the Flame Graph

7 hours ago

Java Flight Recording (JFR) and JDK Mission Control (JMC) are used to identify performance issues in a demo app, showing improvements from 1,198ms to 239ms, heap reduction from 1GB to 139MB, and fewer GC pauses.
Key performance fixes include replacing O(n²) streams in loops with single-pass accumulations, using StringBuilder for string concatenation, and caching regex patterns to avoid recompilation.
Profiling revealed hidden bottlenecks like String.format() in hot paths and thread contention at high concurrency, emphasizing the need to fix issues incrementally and re-profile after each change.
The workflow involves starting with JFR overview, analyzing heap/CPU/contention, applying targeted fixes, and re-running tests to uncover new issues, leading to compound performance gains at scale.

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