Re: Startup cost of sequential scan

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Whose mental model? I guess the Tom Lane mind is the canonical one
> for this project, but I'm not sure that it entirely agrees with mine.

Since the fact that we have a notion of startup cost at all is entirely my
fault, I don't feel shy about claiming to have the authoritative view of
what it means.

(Whether that's adequately documented is another question :-()

> IIRC, it was previously proposed that we ought to charge
> random_page_cost for the first block of a sequential scan, because at
> present the cost of fetching 1 block differs depending on whether we
> are fetching it from a heap or an index, which seems unprincipled.

That might well be a sane thing to do ... but it'd still be part of run
cost not startup cost.

regards, tom lane