Re: again on index usage

"Zeugswetter Andreas SB SD" <ZeugswetterA(at)spardat(dot)at> writes:
> I cannot really see how 284 rows can have an estimated index cost of 100506 ?

The estimated number of indexscanned rows is more like 50k. The number
you are looking at includes the estimated selectivity of the
non-indexable WHERE clauses, too.

> What is actually estimated wrong here seems to be the estimated
> effective cache size, and thus the cache ratio of page fetches.

Good point, but I think the estimates are only marginally sensitive
to estimated cache size (if they're not, we have a problem, considering
how poorly we can estimate the kernel's disk buffer size). It would
be interesting for Daniel to try a few different settings of
effective_cache_size and see how much the EXPLAIN costs change.

regards, tom lane