Redis Cache Overload Kills Database
Redis saved our database. Until it killed it.
What happened:
- Traffic spike: 50K requests/second
- Redis hit 100% CPU
- Cache misses started cascading
- All 50K requests hit the database directly
- Database died within 30 seconds
Root cause:
We had no circuit breaker. When Redis struggled, we didn't gracefully degrade—we just hammered the database with everything Redis couldn't handle.
The fix:
- Circuit breaker pattern: If Redis is slow, return stale data or error—don't hit the database
- Redis Cluster for horizontal scaling
- Connection pooling with timeouts
- Load shedding when approaching capacity
Lesson: Your cache is not just a performance optimization. It's a critical component. When it fails, you need a plan that doesn't involve destroying your database.