Of course it is and there is. Generally DBMSs are not handling 1 request at a time. Indeed such a DBMS wouldn’t be taken seriously. All of them support running run multiple requests concurrently. This is where io_uring is really important because it lets one thread schedule I/O to satisfy one request and resume processing a different request.

Requests are also not I/O bound - you have a mix of CPU work to figure out where to issue the I/O and to manage the cache buffers on completion and read whatever information you need from the buffer pulled in.

But sure, if all your DBMS is going to be doing is one point lookup at a time then there’s no benefit. But even non trivial SQL queries will surprise you because you can get complicated IO famous (eg checking the index which then tells you multiple blocks to look through which you can do concurrently).

TLDR: unless your DBMS is ass slow, pread isn’t sufficient to get good throughput. And at that point it’s irrelevant if a single preadv is faster than io_uring.