>
> > The file I/O itself can be based on the fastpath
> > interface.
>
> What's the 'fastpath interface'?
>
The interface between PG backend and libpq that is for example used for
COPY command. (Simplification) this intarface directly connect two routines
between backend and frondend without standard "the path of query".
Look at src/backend/tcop/fastpath.c
Karel