I've always wondered why I haven't seen a DBMS built as a unikernel. A DBMS is already a "managed runtime" for data, with its own memory allocator, scheduler, filesystem (in some sense), etc. And you're almost always going to want to run a DBMS "workload" on its own dedicated hardware/VM, anyway, for predictability.

So why not just take that set of DBMS services and put them in ring-0, where they won't need any context-switch overhead, will have fine-grained control over their own queuing for kernel resources, and where they can pass data structures by reference all the way from the network to the disk and back?

In Linux, we already have Open-iSCSI, which just has the control plane in userspace, while the data plane is entirely a Linux kernel service, gaining it all these advantages. This architecture works very well there; I'm unclear on why others attempting to provide the higher-level "data-management solutions", with the same high-throughput/low-latency requirements, haven't copied it.