Manfred Koizar <mkoi-pg@aon.at> writes:
> Cutting down the number of heap page fetches if PF1 * L > P and P <
> effective_cache_size seems like an obvious improvement, but I was not
> able to figure out where to make this change. Maybe it belongs into
> costsize.c near
> run_cost += outer_path_rows *
> (inner_path->total_cost - inner_path->startup_cost) *
> joininfactor;
I've been intending for some time to try to restructure the cost
estimator so that repeated indexscans can be costed more accurately.
Within the context of the heap-fetch-estimating algorithm, I think
the entire execution of a nestloop-with-inner-index-scan could probably
be treated as a single scan. I'm not sure how we adjust the estimates
for the index-access part, though clearly those are too high as well.
This doesn't seem to be a localized change unfortunately. Certainly
costsize.c can't do it alone.
regards, tom lane