Cache invalidation storm from backfill
Your product pages are served from a read-through cache (Redis, per-product key, 1h TTL); on a DB write you publish an invalidation that deletes the affected key. At 13:00 a backfill started normalizing a field on all 50M products, updating ~5k rows/sec. Within minutes the database CPU pegs at 100%, page p99 spikes to seconds, and the cache hit rate craters — even for products the backfill hasn't touched. Dashboards: Redis healthy, DB connections maxed, query rate to the DB is ~50x baseline. How do you triage and stop the meltdown?
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.