On Fri, May 8, 2026 at 2:10 PM zengman <[email protected]> wrote:
>
> Hi all,
>
> I noticed that the following SQL statement triggers the error message `cache
> lookup failed for label`.
>
> ```sql
> CREATE TABLE vt (id text PRIMARY KEY, name text, age int);
> CREATE TABLE et (id text PRIMARY KEY, src text REFERENCES vt(id), dst text
> REFERENCES vt(id));
> INSERT INTO vt VALUES ('a', 'Alice', 30), ('b', 'Bob', 25);
> INSERT INTO et VALUES ('e1', 'a', 'b');
>
> CREATE PROPERTY GRAPH g
> VERTEX TABLES (vt LABEL l1 PROPERTIES (name) LABEL l2 PROPERTIES (name,
> age))
> EDGE TABLES (et SOURCE KEY (src) REFERENCES vt(id) DESTINATION KEY (dst)
> REFERENCES vt(id));
>
> CREATE VIEW v1 AS SELECT * FROM GRAPH_TABLE(g MATCH (a IS l2)-[e IS et]->(b
> IS l2) COLUMNS (a.name, a.age, b.name AS bname));
>
> ALTER PROPERTY GRAPH g ALTER VERTEX TABLE vt DROP LABEL l2;
> SELECT * FROM v1;
> ```
>
> Here are the actual test results; it appears to be caused by missing
> dependency information.
>
> ```sql
> test=# CREATE TABLE vt (id text PRIMARY KEY, name text, age int);
> CREATE TABLE
> test=# CREATE TABLE et (id text PRIMARY KEY, src text REFERENCES vt(id), dst
> text REFERENCES vt(id));
> CREATE TABLE
> test=# INSERT INTO vt VALUES ('a', 'Alice', 30), ('b', 'Bob', 25);
> INSERT 0 2
> test=# INSERT INTO et VALUES ('e1', 'a', 'b');
> INSERT 0 1
> test=# CREATE PROPERTY GRAPH g
> VERTEX TABLES (vt LABEL l1 PROPERTIES (name) LABEL l2 PROPERTIES (name,
> age))
> EDGE TABLES (et SOURCE KEY (src) REFERENCES vt(id) DESTINATION KEY (dst)
> REFERENCES vt(id));
> CREATE PROPERTY GRAPH
> test=# CREATE VIEW v1 AS SELECT * FROM GRAPH_TABLE(g MATCH (a IS l2)-[e IS
> et]->(b IS l2) COLUMNS (a.name, a.age, b.name AS bname));
> CREATE VIEW
> test=# ALTER PROPERTY GRAPH g ALTER VERTEX TABLE vt DROP LABEL l2;
> ALTER PROPERTY GRAPH
> test=# SELECT * FROM v1;
> 2026-05-08 15:38:37.121 CST [175953] ERROR: cache lookup failed for label
> 16472
> 2026-05-08 15:38:37.121 CST [175953] STATEMENT: SELECT * FROM v1;
> ERROR: cache lookup failed for label 16472
> test=#
> ```
>
> I've made some minor modifications; this is my diffs file. I'm not sure if
> anything is missing, so feel free to add to or supplement it.
Thanks for the report and the fix. Can you please create a patch/diff
file and attach it to the email please? It's easy to apply an
attachment than copying diff to a file and then applying it.
Please find some comments.
>
> ```c
> diff --git a/src/backend/catalog/dependency.c
> b/src/backend/catalog/dependency.c
> index fdb8e67e1f5..6a73b74fc9b 100644
> --- a/src/backend/catalog/dependency.c
> +++ b/src/backend/catalog/dependency.c
> @@ -2247,6 +2247,22 @@ find_expr_references_walker(Node *node,
> context->addrs);
> /* fall through to examine substructure */
> }
> + if (IsA(node, GraphLabelRef))
> + {
> + GraphLabelRef *lref = (GraphLabelRef *) node;
> +
> + add_object_address(PropgraphLabelRelationId, lref->labelid, 0,
> + context->addrs);
> + return false;
> + }
> + if (IsA(node, GraphPropertyRef))
> + {
> + GraphPropertyRef *gpr = (GraphPropertyRef *) node;
> +
> + add_object_address(PropgraphPropertyRelationId, gpr->propid,
> 0,
> + context->addrs);
> + return false;
> + }
> else if (IsA(node, Query))
> {
> /* Recurse into RTE subquery or not-yet-planned sublink
> subquery */
> @@ -2277,9 +2293,31 @@ find_expr_references_walker(Node *node,
> switch (rte->rtekind)
> {
> case RTE_RELATION:
> +
> add_object_address(RelationRelationId, rte->relid, 0,
> +
> context->addrs);
> + break;
> case RTE_GRAPH_TABLE:
>
> add_object_address(RelationRelationId, rte->relid, 0,
>
> context->addrs);
> +
> + if (rte->graph_pattern)
> + {
> + GraphPattern *gp =
> rte->graph_pattern;
> + ListCell *lc1;
> +
> + foreach(lc1,
> gp->path_pattern_list)
> + {
> + List *path_term
> = lfirst_node(List, lc1);
> + ListCell *lc2;
> +
> + foreach(lc2,
> path_term)
> + {
> +
> GraphElementPattern *gep = lfirst_node(GraphElementPattern, lc2);
> +
> +
> find_expr_references_walker(gep->labelexpr, context);
> + }
> + }
> + }
You could use foreach_node() instead of foreach(). But I am wondering
whether we can directly call find_expr_references_walker() on
rte->graph_pattern. We need to walk rte->graph_table_columns as well.
> break;
> case RTE_JOIN:
>
> ```
>
>
> Final running results
>
> ```sql
> test=# CREATE TABLE vt (id text PRIMARY KEY, name text, age int);
> CREATE TABLE et (id text PRIMARY KEY, src text REFERENCES vt(id), dst text
> REFERENCES vt(id));
> INSERT INTO vt VALUES ('a', 'Alice', 30), ('b', 'Bob', 25);
> INSERT INTO et VALUES ('e1', 'a', 'b');
>
> CREATE PROPERTY GRAPH g
> VERTEX TABLES (vt LABEL l1 PROPERTIES (name) LABEL l2 PROPERTIES (name,
> age))
> EDGE TABLES (et SOURCE KEY (src) REFERENCES vt(id) DESTINATION KEY (dst)
> REFERENCES vt(id));
>
> CREATE VIEW v1 AS SELECT * FROM GRAPH_TABLE(g MATCH (a IS l2)-[e IS et]->(b
> IS l2) COLUMNS (a.name, a.age, b.name AS bname));
The patch needs a test. graph_table.sql already has some view
definitions, some of them using elements with multiple labels. Can you
please add a test using those views? For example after CREATE VIEW
customer_us, you could add a statement dropping label list_items from
all of the elements associated with that label. I guess
pg_get_viewdef() itself should throw an error with the fix, but you
could select from that view as well, if necessary. We also need a test
for drop property. Remember that the property is completely dropped
from a property graph only when it is dropped from all the labels
containing that property. Please apply patches from [1] before adding
tests to your patch. With those patches added your test queries above
will throw a different error.
[1]
https://www.postgresql.org/message-id/caexhw5tccqhgdefbtkwqe7bdqcuxhppsqogipl7vpf0epck...@mail.gmail.com
--
Best Wishes,
Ashutosh Bapat
