Problems / Design a product, medium
Design a live leaderboard from an empty canvas: score updates into a sorted set, top-100 and my-rank reads in milliseconds, and every score persisted to a database.
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Request types to route: score (50%, write), top (30%, read), rank (20%, read). Budget: $3,000 a month.
You start from an empty canvas. When you run the tests, each one simulates your design with its own traffic and failures:
| Test | What it does | Passes when |
|---|---|---|
| Normal day | The normal day: the traffic in the brief, nothing broken. | Success ≥ 99.9%; p99 latency ≤ 30 ms (score); p99 latency ≤ 30 ms (top); p99 latency ≤ 30 ms (rank) |
| Season finale | At 5 s the season’s last match ends: traffic triples for 8 s. | Success ≥ 99%; p99 latency ≤ 60 ms (score); p99 latency ≤ 60 ms (rank) |
| Database 10× slower | At 5 s the main database on the request path answers 10× slower for 8 s. | Success ≥ 99%; p99 latency ≤ 30 ms (score) |
| A server dies | At 4 s one server of the first app service on the request path dies for 10 s. | Success ≥ 99% |
| Budget: $3,000/month | The normal day's design must cost at most $3,000 a month. | Cost ≤ $3,000/month |