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From: Richard Guo <guofenglinux@gmail.com>
Date: Thu, 29 Jan 2026 15:44:24 +0900
Message-ID: <CAMbWs4--NuEUFE_xTo991TRXaZryE29jarJPDnVxoaQOYdt7tA@mail.gmail.com>
Subject: Re: pg_plan_advice
To: Lukas Fittl <lukas@fittl.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, 
	Jacob Champion <jacob.champion@enterprisedb.com>, Dian Fay <di@nmfay.com>, 
	Matheus Alcantara <matheusssilv97@gmail.com>, Jakub Wartak <jakub.wartak@enterprisedb.com>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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Precedence: bulk

> On Wed, Jan 28, 2026 at 6:41=E2=80=AFPM Tom Lane <tgl@sss.pgh.pa.us> wrot=
e:
> > skink's not happy:
> >
> > =3D2162940=3D=3D VALGRINDERROR-BEGIN
> > =3D=3D2162940=3D=3D Conditional jump or move depends on uninitialised v=
alue(s)
> > =3D=3D2162940=3D=3D    at 0x434D366: cost_material (costsize.c:2593)
> > =3D=3D2162940=3D=3D    by 0x436E7E9: materialize_finished_plan (createp=
lan.c:6531)
> > =3D=3D2162940=3D=3D    by 0x4383054: standard_planner (planner.c:533)
> > ...
> > =3D=3D2162940=3D=3D    by 0x44CD09D: ProcessUtility (utility.c:525)
> > =3D=3D2162940=3D=3D  Uninitialised value was created by a stack allocat=
ion
> > =3D=3D2162940=3D=3D    at 0x436E76A: materialize_finished_plan (createp=
lan.c:6506)

FWIW, the following related code in reparameterize_path() seems unsafe
to me:

    spath =3D reparameterize_path(root, spath,
                                required_outer,
                                loop_count);
    enabled =3D
        (mpath->path.disabled_nodes <=3D spath->disabled_nodes);
    if (spath =3D=3D NULL)
        return NULL;
    return (Path *) create_material_path(rel, spath, enabled);

I think we should access spath->disabled_nodes until after we have
verified that spath is not NULL.

Also, it's not quite clear to me why create_material_path (and
cost_material) requires the "enabled" parameter.  I couldn't find any
comments on this, so it might be worth adding some comments here.

- Richard