core practice · coding problem
Cache stampede
Hot key expires, 1000 requests miss together. Name two mitigations.
The mechanism
A cache trades memory and staleness for speed. The hard parts are not the hit — they are invalidation, the stampede when a hot key expires, and deciding how stale is acceptable.
Expected evidence
Probabilistic early expiry, request coalescing/singleflight, mutex per key.
Try this drill in the practice workspace →
Hints when you need them
- TTL jitter spreads expiry.
- One backend fetch serves many waiters.
Watch for these mistakes
- Cache-aside with no stampede protection on a hot key
- No TTL, so stale data lives forever
- Caching per-user data in a shared key