Memory-mapped (MMAP) file I/O is an OS-provided feature that maps the contents of a file on secondary storage into a program’s address space. The program then accesses pages via pointers as if the file resided entirely in memory. The OS transparently loads pages only when the program references them and automatically evicts pages if memory fills up. MMAP‘s perceived ease of use has seduced database management system (DBMS) developers for decades as a viable alternative to implementing a buffer p...