Advanced Debugging

For problems that only appear in production (and can't be easily reproduced locally), two techniques go beyond pdb:

• Structured logging — logging with consistent, searchable fields (logging.info("payment failed", extra={"user_id": 42})) instead of free-form text, so a real incident can be traced through millions of log lines.
• Application performance monitoring (APM) tools capture a timeline of exactly what a slow or failed request did, across every function and database call it touched.

The underlying discipline is the same as Level 1's debugging lesson — reproduce, narrow down, fix — just with better tools for problems too large or too rare to step through by hand.