Developer Fixes Redis Cache Stampede That Spiked API Latency to 3,200ms

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A high-traffic financial affiliate dashboard built on Node.js, Express, and Redis suffered severe performance degradation during peak traffic due to a cache stampede, also known as the thundering herd problem. When cached keys expired, hundreds of simultaneous requests bypassed Redis and hammered the primary SQL database directly, pushing CPU utilization to nearly 100% and API response times from 45ms to over 3,200ms. The developer resolved the issue by implementing distributed mutex locking via Redis SET NX EX, ensuring only one worker recomputes a query on a cache miss, and adopting a stale-while-revalidate strategy to refresh hot cache entries before expiration. These fixes reduced p99 latency to 38ms and cut peak database CPU load by 82%. Google's Gemini AI was used during post-mortem analysis to identify a potential deadlock risk when Redis connections dropped mid-lock-release, leading to the addition of proper try/finally cleanup blocks.

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