Interesting. When I read your first comment, I didn't realize you meant "bypass kernel" in as wide a scope as you describe here. Usurping CPU scheduling, in particular, was something I didn't think was common practice. Can you name a (presumably commercial) DBMS that represents this kind of "self-manage everything" architecture?
Most of the big "enterprise" OLTP databases are designed this way; the less portable they are, the more likely they are doing deep bypass optimizations. DB2, SQL Server, and similar are bypass designs. Oracle used to be a weird hybrid, due to portability requirements, but since they took control of the hardware I would assume recent versions are mostly pure bypass.
Most commercial analytical databases are not bypass, due in large part to the fact that most of them are based on Postgres, ironically.
