SQLite Forum

How db access is handled by sqlite3?
For reading, yes.  mmap directly maps the OS page cache into process address space using the process page table (in most implementations).

However, writing requires that the library "copy" the page being modified into process private storage for modification before being written to the database.

This should be obvious since if the changes were directly made to the mapped pages, they would be visible to other processes immediately rather than only after commit.