"mmap" in the general case is incredibly useful. There's so much you get "for free" and the UX/DX of reads/writes to it, especially if you're primarily operati

"mmap" in the general case is incredibly useful. There's so much you get "for free" and the UX/DX of reads/writes to it, especially if you're primarily operating on structs instead of raw byte/string data. (Example, reading a file and "reinterpret_cast<>"'ing it from bytes to in-memory struct representations) It's just that for the _particular_ case of a DBMS that relies on optimal I/O and transactionality, the general-purpose kernel implementation of mmap falls short of what you can implement by hand.