This is not what I was referring to, no. When operating a database at huge scale surprising things happen, because everything that can happen will happen. So o

This is not what I was referring to, no. When operating a database at huge scale surprising things happen, because everything that can happen will happen. So operators are interested in ensuring the database behaves well in these extreme circumstances. This isn’t specifically about horizontal scalability, though that is a necessary component. To your point about vertical scalability, no doubt Scylla performs better here. However the details of your mentioned comparison are perhaps misleading, as Cassandra can happily exploit more than 16vCPUs before its performance materially plateaus. While it’s true that the JVM imposes some restrictions, they do not translate to a difference in performance on the order of that claimed in this post. JVMs have also been NUMA-aware for some time. The main explanatory factor is relative investment and focus.