> I have put some printfs into sqlite 3.32.3 and found that when mmap() is being used, there are numerous calls to sqlite30sFetch. > But when :memory: is being used, there are none. > So before getting into the intricacies of kernel mmap implementations, I'd first like to get Sqlite pragma mmap to go through the :memory: code path. The significant difference between those storage arrangement is: mmap necessarily retains backing of the mapped memory by a persistent store and must involve calls to the OS (or interrupts that reach the OS) at times, whereas the :memory: VFS is purely an application-level emulation of a (typically) OS-level file API. The latter has less work to do than the former. I think your desire to get mmap to be as fast as :memory: is due to valuing speed over the modularity that would have to be sacrificed in order to get the speed.