Re: (SQL/PGQ) cache lookup failed for label

> For now I have added a test case exhibiting this behaviour. If we
> commit the test, somebody who comes across this behaviour will know
> why the current behaviour is the way it is and what's the way forward.
> But if we don't commit it, which is ok, they will consider this as
> buggy behaviour and report it. I am fine either way.
>
> As I mentioned earlier, I am creating patches for all outstanding
> issues from the same branch. So the patches attached here do not start
> from 0001, but they apply with git am on the latest master for me
> without any problem.
> 0005 - fixes `cache lookup failed for label`
> 0006 - fixes empty label expression and view behaviour
> 0007 - issue with labels shared by vertex and edges

Hi Ashutosh,

I applied and tested the v20260601 patches on top of master, looks good.

One thing I noticed though -- RemoveRelations() in propgraphcmds.c
cleans up orphaned pg_propgraph_property entries, but the condition
doesn't include drop_label:

```diff
diff --git a/src/backend/commands/propgraphcmds.c b/src/backend/commands/propgraphcmds.c
index cc516e27020..7c8f397afbf 100644
--- a/src/backend/commands/propgraphcmds.c
+++ b/src/backend/commands/propgraphcmds.c
@@ -1638,7 +1638,7 @@ AlterPropGraph(ParseState *pstate, const AlterPropGraphStmt *stmt)
}

/* Remove any orphaned pg_propgraph_property entries */
- if (stmt->drop_properties || stmt->drop_vertex_tables || stmt->drop_edge_tables)
+ if (stmt->drop_label || stmt->drop_properties || stmt->drop_vertex_tables || stmt->drop_edge_tables)
{
foreach_oid(propoid, get_graph_property_ids(pgrelid))
{
```

```sql
postgres(at)zxm-VMware-Virtual-Platform:~/code/postgres$ psql
psql (19beta1)
Type "help" for help.

postgres=# CREATE PROPERTY GRAPH g1
VERTEX TABLES (
v1
LABEL vl1 PROPERTIES (a, b, c)
LABEL vl2 PROPERTIES (a) LABEL vl3 PROPERTIES (a,b)
);
CREATE PROPERTY GRAPH
postgres=# ALTER PROPERTY GRAPH g1 ALTER VERTEX TABLE v1 DROP LABEL vl1;
ALTER PROPERTY GRAPH
postgres=# SELECT oid, pgpname FROM pg_propgraph_property WHERE pgppgid = 'g1'::regclass ORDER BY pgpname;
oid | pgpname
--------+---------
111971 | a
111973 | b
111975 | c
(3 rows)
```

After dropping vl1, b and c are still there even though no label
references them anymore. Not sure if this is worth fixing -- thoughts?

--
regards,
Man Zeng