As a consequence of implementing some of these kernel functions in user space, it is not possible to determine object lifetimes or track mutable references at compile-time. Any object created in memory that bypasses the kernel mechanisms is unsafe as far as Rust is concerned. In a database, the vast majority of your objects are constructed on this type of memory.
You can implement this in Rust, but essentially the entire database kernel will be "unsafe". At which point, why bother with Rust? C++ is significantly more expressive at writing this type of code, and it is not trivial even in C++.
As a consequence of implementing some of these kernel functions in user space, it is not possible to determine object lifetimes or track mutable references at compile-time. Any object created in memory that bypasses the kernel mechanisms is unsafe as far as Rust is concerned. In a database, the vast majority of your objects are constructed on this type of memory.
You can implement this in Rust, but essentially the entire database kernel will be "unsafe". At which point, why bother with Rust? C++ is significantly more expressive at writing this type of code, and it is not trivial even in C++.