Re: [HACKERS] Recognizing range constraints (was Re: Plan for relatively simple query seems to be very inefficient)

John A Meinel <john(at)arbash-meinel(dot)com> writes:
> Actually, I think he was saying do a nested loop, and for each item in
> the nested loop, re-evaluate if an index or a sequential scan is more
> efficient.

> I don't think postgres re-plans once it has started, though you could
> test this in a plpgsql function.

It doesn't, and in any case that's a microscopic view of the issue.
The entire shape of the plan might change depending on what we think
the selectivity is --- much more than could be handled by switching
scan types at the bottom level.

Also, I anticipate that bitmap-driven index scans will change things
considerably here. The range of usefulness of pure seqscans will
drop drastically...

regards, tom lane