Swap thrashing during RDB save
A Redis instance (used as a cache+session store) becomes briefly unresponsive — commands stall for several seconds — every hour on the hour, and clients see timeouts and a thundering retry storm. The instance holds ~12GB of data on a 16GB host with no maxmemory set and swap enabled. The stalls line up exactly with the scheduled RDB save (`save 3600 ...`) at the top of each hour: during the save you see memory usage briefly spike toward the host limit, swap si/so activity, and high iowait. 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 40 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.