Search timeout with type mismatch
A search endpoint that filters customers by a phone-number field started timing out after a deploy that 'just changed a query.' `EXPLAIN ANALYZE` shows a sequential scan over the 50M-row `customers` table even though there's a btree index on `phone`. The column is `varchar` but the new code passes the parameter as an integer (`bigint`). Older queries on the same column are still fast and use the index. CPU climbs whenever the endpoint is hit. Triage and mitigate.
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 30 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.