Problems / Design a product, medium
Design search autocomplete from an empty canvas: the top 10 completions for every keystroke within 50 ms at p99, rebuilt offline from a stream of finished searches.
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Request types to route: suggest (90%, read), log (10%, write). Budget: $2,400 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 ≤ 50 ms (suggest) |
| Breaking news | At 5 s a breaking story sends everyone to the search box: traffic triples for 8 s. | Success ≥ 99%; p99 latency ≤ 80 ms (suggest) |
| Cache flushed | At 5 s the cache on the request path is emptied, as after a restart or a bad deploy. | Success ≥ 99%; p99 latency ≤ 100 ms (suggest) |
| A server dies | At 4 s one server of the first app service on the request path dies for 10 s. | Success ≥ 99%; p99 latency ≤ 60 ms (suggest) |
| Budget: $2,400/month | The normal day's design must cost at most $2,400 a month. | Cost ≤ $2,400/month |