Re: index cost estimation

Le mercredi 6 juillet 2022, 16:52:09 CEST Ronan Dunklau a écrit :
> Le mercredi 6 juillet 2022, 16:41:29 CEST Tom Lane a écrit :
> > Hm, so it'd seem this probably could happen when comparing *any*
> > non-btree index to a btree index, because I don't think we are
> > particularly careful with CPU cost estimation for any of the
> > other index types.  If we do something about this, we probably
> > have to look at all of them.
> 
> For gist and sp-gist, a descent cost is taken into account, by estimating 
the
> tree height so that particular effect is mitigated. Whether the cpu cost
> estimation is sensible regarding to btree is another topic, but at least the
> index cost doesn't vanish when inside a loop.
> 
> Hash, brin and bloom are quite different, so maybe another examination would 
be
> required but probably outside the scope of this bug report.

Here is a patch tentatively addressing the problem. I'm not sure what I'm 
doing with the number of searched entries is right though.


-- 
Ronan Dunklau