Haven't looked through the scylla codebases, but can definitely recommend the latter two.

Strongly seconded. Beyond the language aspects, the scylladb projects are full of instructive architectural ideas and design choices.

A good blog I wrote up based on Avi Kivity's talk at Core C++ 2019. Also our blog on using io_uring and eBPF:

• https://www.scylladb.com/2020/03/26/avi-kivity-at-core-c-201... • https://www.scylladb.com/2020/05/05/how-io_uring-and-ebpf-wi...