The problem turns out to be that the CPU is holding up data access. For those brought up with mechanical storage it is a shock, as disks are thousands of times slower than the CPU, but modern storage is solid state, just like the CPU.
Professor Zwaenepoel's software is called KVell (Key Value and North American slang for happy and proud). This reminded me of what Canberra start-up Instaclustr, do with Apache Cassandra. There are many articles for Cassandra setting for SSDs.
This was an excellent seminar to be back on campus for. It challenged assumptions from my earliest training at the ABS decades ago.
ps: ANU events follow Oxford Time: "Classes commence at five minutes past the published start time and conclude five minutes before the published end time."(Policy: Timetable, ANU, Paragraph 6, 2019).