Thread

Re: [Bug]Assertion failure in LATERAL GRAPH_TABLE with multi-label pattern

SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com> — 2026-05-12T17:41:53Z

HI,

On Tue, May 12, 2026 at 4:15 AM Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
wrote:

> On Thu, May 7, 2026 at 9:43 AM SATYANARAYANA NARLAPURAM
> <satyanarlapuram@gmail.com> wrote:
> >
> > Hi hackers,
> >
> > A LATERAL GRAPH_TABLE whose pattern matches more than one path query
> > fails with the assert
> >
> > TRAP: failed Assert("!bms_is_member(rti, lateral_relids)"), File:
> "initsplan.c", Line: 1428, PID: 3586144
> > postgres: postgres postgres [local]
> SELECT(ExceptionalCondition+0x70)[0x63488e3cc070]
> > postgres: postgres postgres [local]
> SELECT(create_lateral_join_info+0x468)[0x63488e14ac28]
> > postgres: postgres postgres [local]
> SELECT(query_planner+0x13a)[0x63488e14dfca]
> >
> > Repro:
> > SELECT v1.vname, gt.aname
> >   FROM v1, LATERAL (SELECT * FROM GRAPH_TABLE (g1 MATCH (a IS vl1 | vl2
> WHERE a.vprop1 = v1.vprop1) COLUMNS (a.vname AS aname)) g) gt
> >   ORDER BY 1, 2;
> >
> > Single-label GRAPH_TABLE with the same outer reference works fine.
> > rewriteGraphTable() turns the GRAPH_TABLE RTE into a subquery RTE and
> > bumps outer Vars by one sublevel.  When the pattern produces multiple
> > path queries, generate_setop_from_pathqueries() wraps each one in
> > another subquery RTE for the UNION ALL but does not bump again, so the
> > lateral reference collapses onto GRAPH_TABLE's own RTE.
>
> + /* Wrapping lquery in a subquery RTE adds one query level, so bump
> + * outer-level Vars accordingly. */
> + IncrementVarSublevelsUp((Node *) lquery, 1, 1);
> +
>
> Multiline comments start with /* and end with */ on separate lines
> respectively.
>
> From the comment it feels like we will add as many varlevels as the
> depth of setop tree, since we will add a subquery RTE for each setop
> level. In reality all the legs of the setop tree will be at the same
> varlevel. A better comment would be "Vars in each path query are one
> level away from the setop query combining them.".
>
> The connection between varlevelsup, addition of subquery RTE and the
> assertion failure isn't clear. Assertion failure indicates that the
> relation being examined has lateral reference to itself which boils
> down to range table entry index but the varlevelsup is about depth of
> a given query. The connection between these two seemingly different
> things needs to be explained in the commit message. Though the code
> changes fix the problem, there may be a better place to increment
> varlevels up. That will be clear once the connection is clear.
>
> >
> > Tried fixing this by bumping each lquery's sublevels by 1 before the
> addRangeTableEntry
> > ForSubquery() wrap.  Single-pathquery queries skip this path entirely.
> >
> > Attached a patch with the tests.
> >
>
> Do we need both the tests? The second one has no label expression
> which means it will try all the labels. So the test will reproduce the
> bug only when there are multiple labels. The first test explicitly
> adds the multi-label pattern. I think we should just leave the first
> one and remove the second one. Also this test should be placed in the
> section which tests other lateral references. myshop property graph
> has two sets of elements that share a label - order and wishlist,
> order_items and wishlist_items.
>

Thanks for reviewing, will address the comments shortly.