As I mentioned memory access latency - I just posted my old article series about measuring RAM access performance (using different database workloads) to HN and looks like it even made it to the front page (nice):
We've made Scylla as async, shared nothing as possible, and we've also started adding C++20 coroutines (to replace futures/promises). We'll be doing more of that in 2021.
https://news.ycombinator.com/item?id=25863093