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In-Reply-To: 
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From: Amit Langote <amitlangote09@gmail.com>
Date: Thu, 25 Jun 2026 21:21:15 +0900
Message-ID: 
 <CA+HiwqGOcb+ZHon5Tnm7syFW8+t-wa5rBzrSoTgh4LeVt4MrZA@mail.gmail.com>
Subject: Re: BUG #19484: Segmentation fault triggered by FDW
To: Etsuro Fujita <etsuro.fujita@gmail.com>
Cc: Richard Guo <guofenglinux@gmail.com>,
 Matheus Alcantara <matheusssilv97@gmail.com>,
	Ayush Tiwari <ayushtiwari.slg01@gmail.com>,
 Rafia Sabih <rafia.pghackers@gmail.com>,
	798604270@qq.com, pgsql-bugs@lists.postgresql.org,
	Amit Langote <amitlan@postgresql.org>
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 <https://www.postgresql.org/message-id/CA%2BHiwqGOcb%2BZHon5Tnm7syFW8%2Bt-wa5rBzrSoTgh4LeVt4MrZA%40mail.gmail.com>
Precedence: bulk

On Thu, Jun 25, 2026 at 8:47=E2=80=AFPM Amit Langote <amitlangote09@gmail.c=
om> wrote:
> On Thu, Jun 25, 2026 at 3:15=E2=80=AFPM Etsuro Fujita <etsuro.fujita@gmai=
l.com> wrote:
> > On Thu, Jun 25, 2026 at 8:24=E2=80=AFAM Amit Langote <amitlangote09@gma=
il.com> wrote:
> > > On Thu, Jun 25, 2026 at 2:02=E2=80=AFAM Etsuro Fujita <etsuro.fujita@=
gmail.com> wrote:
> > > > This might be nitpicking, but:
> > > >
> > > > +           if (list_length(node->resultRelations) =3D=3D mtstate->=
mt_nrels)
> > > > +               fdw_private =3D (List *) list_nth(node->fdwPrivList=
s, j);
> > > > +           else
> > > > +           {
> > > > +               Index       rti =3D resultRelInfo->ri_RangeTableInd=
ex;
> > > > +               ListCell   *lc1;
> > > > +               ListCell   *lc2;
> > > > +
> > > > +               fdw_private =3D NIL;
> > > > +               forboth(lc1, node->resultRelations, lc2, node->fdwP=
rivLists)
> > > > +               {
> > > > +                   if (lfirst_int(lc1) =3D=3D (int) rti)
> > > > +                   {
> > > > +                       fdw_private =3D (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 remainin=
g
> > > > 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=3Dcrake&br=3DRE=
L_18_STABLE

--=20
Thanks, Amit Langote