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

On Thu, May 7, 2026 at 9:43 AM SATYANARAYANA NARLAPURAM
<satyanarlapuram(at)gmail(dot)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.

--
Best Wishes,
Ashutosh Bapat