You aren't comparing the same program written in two languages. Seastar stuff is...

zigzigzag on Feb 1, 2017 | parent | context | favorite | on: The JVM is not that heavy

You aren't comparing the same program written in two languages. Seastar stuff is written by C++ performance experts who are fanatical about tuning, and does all kinds of unusual far-out things that Cassandra doesn't do to get high performance.