If you investigate what they actually do to achieve those numbers, it's much less simple than just rewriting Cassandra in C++. For example, they use their own TCP stack and make use of vector intrinsics.
so what you mean is that, even after throwing facebook scale resources at java.. it is possible for a <10 people team to get 10X performance over java using the features that you mention.
That's a huge loss of face for java IMHO
Because the JVM JIT, like every other compiler, sucks at developing vectorized algorithms ad-hoc; a task usually carried out by human experts in that?
That is not what I mean. Writing a userspace TCP stack isn't a feature of C++.