Feature store timeouts during backfill
Your ranking service reads ~40 features per request from an online feature store (Redis-backed). At 15:10 the service's error rate climbs to 3% with timeouts, and p99 latency on the feature-fetch step spikes. Dashboards: the feature store's Redis node shows high CPU and a jump in slow-log entries; the keyspace grew sharply after a backfill job started writing a new large feature ('user_event_history') as a big serialized blob per user; client-side connection-pool wait time is up. A backfill of that feature began at 15:00. 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.