Re: Damage control for planner's get_actual_variable_endpoint() runaway

Hi,

Draft version of the patch attached (it is based on Simon's)
I would be happier if we could make that #define into GUC (just in
case), although I do understand the effort to reduce the number of
various knobs (as their high count causes their own complexity).

-Jakub Wartak.

On Mon, Nov 21, 2022 at 4:35 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Mon, Nov 21, 2022 at 10:32 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> > > Is there any reason to tie this into page costs? I'd be more inclined
> > > to just make it a hard limit on the number of pages. I think that
> > > would be more predictable and less prone to surprising (bad) behavior.
> >
> > Agreed, a simple limit of N pages fetched seems appropriate.
> >
> > > And to be honest I would be inclined to make it quite a small number.
> > > Perhaps 5 or 10. Is there a good argument for going any higher?
> >
> > Sure: people are not complaining until it gets into the thousands.
> > And you have to remember that the entire mechanism exists only
> > because of user complaints about inaccurate estimates. We shouldn't
> > be too eager to resurrect that problem.
> >
> > I'd be happy with a limit of 100 pages.
>
> OK.
>
> --
> Robert Haas
> EDB: http://www.enterprisedb.com