Production Bug Forensic Root-Cause Analysis & 5-Whys

You are a Principal Site Reliability Engineer (SRE) and Blameless Incident Commander. I need to conduct a forensic root-cause analysis on a serious production outage or recurring bug. Incident Timeline & Symptoms: 10:14 AM: Marketing sent email campaign to 500k users. 10:18 AM: Web dashboard latency spiked from 150ms to 24,000ms. 10:22 AM: PostgreSQL database CPU hit 100% and connection pool exhausted. 10:40 AM: Database restarted, traffic throttled. Stack Trace / Error Logs / Telemetry: Postgres log: `LOG: duration: 8412.314 ms statement: SELECT * FROM user_notifications WHERE user_id = $1 ORDER BY created_at DESC;` Node.js error: `TimeoutError: ResourceRequest timed out after 10000ms at Pool.acquire` Relevant Code or System Architecture: The notification dropdown component in the web navigation bar triggers `GET /api/notifications` on every page navigation, executing `SELECT * FROM user_notifications WHERE user_id = $1 ORDER BY created_at DESC LIMIT 10`. Deliver an exhaustive SRE Post-Mortem & 5-Whys Analysis: 1. The 5-Whys Root-Cause Tree: Drill down from the superficial symptom (e.g. 504 Gateway Timeout) through intermediate triggers to the foundational systemic failure (procedural, architectural, or testing gap). 2. Mechanism Breakdown: Step-by-step technical explanation of what occurred inside memory, database connection pools, or the event loop during the incident. 3. The Permanent Technical Fix: Specific code, architectural change, or circuit-breaker pattern to ensure this failure mode cannot recur. 4. Blameless Action Items Matrix: Categorized into Prevent, Detect, and Mitigate, with single-owner assignments and timeline estimates.