Cache hit ratio collapses
Over the last 30 minutes your Redis cache (maxmemory set, allkeys-lru eviction) has degraded: hit ratio fell from 95% to 60%, evicted_keys is climbing by tens of thousands per second, the origin DB load is doubling, and Redis p99 GET latency rose from 0.4ms to 9ms. used_memory is pinned at maxmemory. A new feature shipped this morning that caches per-user personalized search results keyed by user_id + a serialized query object, with no explicit TTL. How do you 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 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.