playground
Sharding & Hot Keys
Your database is split across shards by key range. Each shard sustains 5,000 rps. Skew sends a share of all traffic to one hot key on shard 1 — a celebrity profile, a viral post, a flash-sale SKU.
dropped 6.7%
hot shard p99 ∞ (saturated)
sharding guidestep 1/4
→ Set skew to 0% and push traffic above 40k rps.
waiting for you to try it…
120%
s1 🔥
60%
s2
60%
s3
60%
s4
dashed line = shard capacity (5,000 rps)
The takeaway: sharding scales uniform load linearly, but a hot key concentrates on one shard no matter how many you add. Real systems fix this with a cache in front of the hot key, key salting, or moving the hot entity to its own store.
Now design a system that survives this →