Re: BUG #19484: Segmentation fault triggered by FDW

On Thu, Jun 25, 2026 at 8:47 PM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> On Thu, Jun 25, 2026 at 3:15 PM Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)com> wrote:
> > On Thu, Jun 25, 2026 at 8:24 AM Amit Langote <amitlangote09(at)gmail(dot)com> wrote:
> > > On Thu, Jun 25, 2026 at 2:02 AM Etsuro Fujita <etsuro(dot)fujita(at)gmail(dot)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.

And crake turns green:

https://buildfarm.postgresql.org/cgi-bin/show_history.pl?nm=crake&br=REL_18_STABLE

--
Thanks, Amit Langote