Query engine p99 spikes nightly
A self-managed analytics box that colocates a query engine and several batch workers becomes molasses-slow every weeknight around 22:00: p99 on the query engine jumps from 80ms to 12s for ~20 minutes, then recovers on its own. During the window `vmstat 1` shows si/so (swap in/out) in the thousands, CPU is ~60% iowait with low user CPU, and there are no OOM kills in `dmesg`. The box has 64GB RAM and 32GB swap, `vm.overcommit_memory=1` (always overcommit), and a nightly batch job was scaled up last sprint to use more parallel workers. 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.