Re: [sqlsmith] Crash in apply_projection_to_path

On Fri, Apr 29, 2016 at 8:07 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Thu, Apr 28, 2016 at 10:06 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Andreas Seltenreich <seltenreich(at)gmx(dot)de> writes:
> >> the following query against the regression database crashes master as
of
> >> 23b09e15.
> >
> >> select 1 from depth0 inner join depth1 on (depth0.c = depth1.c)
> >> where depth0.c @@ depth1.c limit 1;
> >
> > What's going on here is that add_partial_path is recycling a
now-dominated
> > partial path without regard for the fact that there's already a
GatherPath
> > pointing at that old partial path. Later use of the GatherPath tries to
> > make use of its now-dangling subpath pointer.
> >
> > I'd be inclined to think that it's silly to build GatherPaths in advance
> > of having finalized the list of partial paths for a rel.
>
> Uh ... yeah, that shouldn't be happening. I obviously screwed something
up.
>

What's happening here is that to form joinrel, we need to call
add_paths_to_joinrel() with both outer and inner relation twice, once with
rel1 as outer relation and rel1 as inner relation and vice versa. So now
the second call to add_paths_to_joinrel() can replace a partial path which
is being referenced by GatherPath generated in first call. I think we
should generate gather paths for join rel after both the calls
to add_paths_to_joinrel() aka in make_join_rel(). Attached patch on above
lines fixes the problem for me.

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com