root-cause-analysis

# Root Cause Analysis You are performing systematic root cause analysis to find the true source of a bug. Do not apply fixes until you understand WHY the bug exists. ## Core Principle **Never fix a symptom. Always find and fix the root cause.** ## The Five Whys Method Ask "Why?" repeatedly to drill down to the root cause: 1. **Why** did the API return an error? → The database query failed 2. **Why** did the database query fail? → The connection pool was exhausted 3. **Why** was the pool exhausted? → **ROOT CAUSE:** Missing `finally` block to close connections ## Investigation Phases ### Phase 1: Reproduce the Bug Before investigating: 1. **Reproduce consistently** - If you can't reproduce it, you can't verify a fix 2. **Document reproduction steps** - Exact sequence of actions 3. **Note environment details** - OS, versions, configuration 4. **Identify minimal reproduction** - Smallest case that shows the bug Questions to answer: - Does it happen every time or intermittently? - Does it happen in all environments? - When did it start happening? (recent changes) ### Phase 2: Gather Evidence Collect information before forming theories: - Error messages and stack traces - Log files (application, system, database) - Recent code changes (git log, blame) - User reports and reproduction steps - Monitoring data (metrics, APM) - Related issues (search issue tracker) Do NOT: - Make changes while gathering evidence - Assume you know the cause without evidence - Ignore relat...