I would wish that the whole (disk) I/O mess would be cleaned up. It's just laughable how broken that is across operating systems. And it's supposed to be the back-bone of most operating systems as well.

Also, memory management. Only in very recent years proprietary APIs surfaced in Linux and friends that allow to leverage some of a modern MMUs capabilities (which is good). Meanwhile we still have stupid MM semantics like fixed / non-reversible allocation commits.

> The database people would love to have well-defined semantics like this.

Yes. Yes they would.

Right now there is no way in no operating system to actually do asynchronous disk IO. You can do an equivalent of write(2) asynchronously, at least on Linux, Windows and I think SunOS, but in all of them it's not really asynchronous; they will run extent allocation synchronously which can -worst case- mean multiple disk read/write cycles. This of course means that for many applications that could make use of async write actually need to use threads and queues for doing it.