Re: BUG #19484: Segmentation fault triggered by FDW

Fujita-san,

On Thu, Jun 25, 2026 at 3:15 PM Etsuro Fujita <etsuro.fujita@gmail.com> wrote:
> On Thu, Jun 25, 2026 at 8:24 AM Amit Langote <amitlangote09@gmail.com> wrote:
> > On Thu, Jun 25, 2026 at 2:02 AM Etsuro Fujita <etsuro.fujita@gmail.com> wrote:
> > > This might be nitpicking, but:
> > >
> > > +           if (list_length(node->resultRelations) == mtstate->mt_nrels)
> > > +               fdw_private = (List *) list_nth(node->fdwPrivLists, j);
> > > +           else
> > > +           {
> > > +               Index       rti = resultRelInfo->ri_RangeTableIndex;
> > > +               ListCell   *lc1;
> > > +               ListCell   *lc2;
> > > +
> > > +               fdw_private = NIL;
> > > +               forboth(lc1, node->resultRelations, lc2, node->fdwPrivLists)
> > > +               {
> > > +                   if (lfirst_int(lc1) == (int) rti)
> > > +                   {
> > > +                       fdw_private = (List *) lfirst(lc2);
> > > +                       break;
> > > +                   }
> > > +               }
> > > +           }
> > >
> > > I'd put the if-test outside of the outer loop to save cycles.
> >
> > Right, it's loop-invariant. v3 attached computes a boolean
> > (nopruning), like labeltargets, once before the loop and uses it
> > inside.
> >
> > > Other than that v2 looks good to me.
> > >
> > > (The forboth loop actually causes an n-squared calculation, but it's
> > > done only when pruning occurs, in which case the number of remaining
> > > result relations would be reduced, so that wouldn't be a problem.)
> >
> > Right, though strictly the inner forboth scans node->resultRelations,
> > which pruning leaves at its original length, so it's the original
> > relation count that bounds the scan rather than the reduced one.
> > Either way it's EXPLAIN-only with small counts, so it's not a concern.
>
> That's right.
>
> The v3 patch looks good to me.  Thanks for updating the patch!

Pushed, thanks for checking.

-- 
Thanks, Amit Langote