The "Cache Stampede" Catastrophe
When a popular product cache key expires in the middle of a marketing broadcast, 10,000 simultaneous users will all query the underlying MySQL database at the exact same millisecond. This causes catastrophic connection exhaustion and total server crashes.
Mitigation Strategies
- Probabilistic Early Expiration (XFetch): Refresh cache keys asynchronously in background workers before they expire.
- Atomic Mutex Locking: Only the first requesting worker gets permission to query the database and rebuild the cache; other workers wait 50ms and consume the new cache.
- Dedicated Redis Instances: Run separate Redis instances for session storage, cache tags, and background queue workers so queue backlogs never degrade website browsing speed.
