● Free · no signup · ~5 min
Try a system design drill
One focused, interview-style prompt. Write a short answer and an AI interviewer grades it in seconds.
The prompt
A read-heavy feed service caches every user's timeline in Redis and rebuilds it on every write. Traffic from a few celebrity accounts is melting the cache. What's the bottleneck, and how do you fix it?
Celebrity fan-out is the pain pointName the trade-off of your fix
Your answerFill in each line — schema, bullets, or prose.
Bottleneck ◯·Fix ◯·Trade-off ◯
No diagram needed for a drill — that's what the full interview is for.