Re: Make the qual cost on index Filter slightly higher than qual cost on index Cond.

Thanks all of you for your feedback.

On Fri, May 29, 2020 at 9:04 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> > On Wed, May 27, 2020 at 09:58:04PM +0800, Andy Fan wrote:
> >> so we need to optimize the cost model for such case, the method is the
> >> patch I mentioned above.
>
> > Making the planner more robust w.r.t. to estimation errors is nice, but
> > I wouldn't go as far saying we should optimize for such cases.
>
> Yeah, it's a serious mistake to try to "optimize" for cases where we have
> no data or wrong data. By definition, we don't know what we're doing,
> so who's to say whether we've made it better or worse?

Actually I think it is a more robust way.. the patch can't fix think all
the impact
of bad statistics(That is impossible I think), but it will make some
simple things
better and make others no worse. By definition I think I know what we are
doing
here, like what I replied to Tomas above. But it is possible my think is
wrong.

> The other serious error we could be making here is to change things on
> the basis of just a few examples. You really need a pretty wide range
> of test cases to be sure that you're not making things worse, any time
> you're twiddling basic parameters like these.
>
>
I will try more thing with this direction, thanks for suggestion.

--
Best Regards
Andy Fan