Explore advanced .NET debugging techniques through a real-world investigation at Criteo, where 150 billion requests are processed daily across 4000+ front-end servers. Follow the Performance team's journey from early detection to final fix, learning valuable insights, common pitfalls, and effective tools. Discover how to use metrics for issue detection and assessment, leverage profilers for initial assumptions, dive into CLR data structures using decompilers, WinDBG, and SOS, and automate memory dump analysis with ClrMD when WinDBG falls short. Gain practical knowledge on handling unexpected service behavior post-release, including techniques like checking source code, instance methods, and meta metrics. Understand the importance of mindset, third chance exceptions, lock catch blocks, and curse loops in debugging complex systems.