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.

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Tags: #Redis #Caching #Database #Performance