Cart endpoint p99 regression
After a deploy at 10:00, GET /cart p99 regressed from 90ms to 700ms; p50 went from 40ms to 60ms (mild). Throughput and error rate are unchanged. Distributed traces for slow requests show the time is spent in many small, sequential database calls — a slow request makes ~150 round-trips to the DB, each ~3ms, while a fast request makes ~5. The deploy 'added per-line-item promotional pricing.' Carts vary in size; big carts are slow, small carts are fine. Triage and explain the regression precisely.
What a strong answer looks like
Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.
0:00 of about 35 min
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.