Paul Tuckfield <paul(at)tuckfield(dot)com> writes:
> In the case of select count(*), one optimization is to do a scan of the
> primary key, not the table itself, if the table has a primary key. In a
> certain commercial, lesser database, this is called an "index fast full
> scan". It would be important to scan the index in physical order
> (sequential physical IO) and not in key order (random physical IO)
That won't work because you still have to hit the actual tuple to
determine visibility.
-Doug