Re: BUG #19435: Error: "No relation entry for relid 2" Triggered by Complex Join with Self-Referencing Tables

Alexander Korotkov <aekorotkov@gmail.com> 于2026年3月18日周三 01:46写道：
>
> On Tue, Mar 17, 2026 at 3:30 PM Tender Wang <tndrwang@gmail.com> wrote:
> > Kirill Reshke <reshkekirill@gmail.com> 于2026年3月17日周二 21:24写道：
> > >
> > > On Tue, 17 Mar 2026 at 18:20, Tender Wang <tndrwang@gmail.com> wrote:
> > > Yes, it looks like your analysis is valid. Will you share a patch for
> > > updating `clause` ?
> > >
> > Sorry, it's already the middle of the night here, so I'm afraid I
> > don't have much time to work on this right now.
>
> Thank you for your research.  I've written a simple draft patch.  It
> fixes the reported case, but I doubt it is correct in general.  I'll
> continue the investigation.
The cause of this bug is doing the following statement:
...
ChangeVarNodesWalkExpression((Node *) rinfo->clause, context);
...
in replace_relid_callback().

The rinfo->clause is only Var(tom1.col_bool), sorry I typoed it to "
ON tom1.col_bool IS NOT NULL", in my first reply email.
See expression_tree_walker_impl(), it does nothing if the node is just
a Var node.
So I think whether we can add logic in ChangeVarNodesWalkExpression() as below:

...
if (node && IsA(node, Var))
    {
        Var        *var = (Var *) node;

        if (var->varlevelsup == context->sublevels_up)
        {
            if (var->varno == context->rt_index)
                var->varno = context->new_index;
            var->varnullingrels = adjust_relid_set(var->varnullingrels,
                                                   context->rt_index,
                                                   context->new_index);
            if (var->varnosyn == context->rt_index)
                var->varnosyn = context->new_index;
        }
        return false;
    }
    else
        return expression_tree_walker(node,
                                      ChangeVarNodes_walker,
                                      (void *) context);
...

I tried the above fix, no error again.  But I got a plan like this:
                                        QUERY PLAN
-------------------------------------------------------------------------------------------
 Nested Loop Left Join  (cost=0.00..115164616.71 rows=7458350250 width=4)
   ->  Seq Scan on pg_table_a tom3  (cost=0.00..34.70 rows=2470 width=0)
   ->  Materialize  (cost=0.00..99509.82 rows=3019575 width=0)
         ->  Nested Loop Left Join  (cost=0.00..75564.95 rows=3019575 width=0)
               Join Filter: tom2.col_bool
               ->  Seq Scan on pg_table_a tom2  (cost=0.00..34.70
rows=2445 width=5)
                     Filter: ((col_bool IS NOT NULL) AND (col_bool IS NOT NULL))
               ->  Materialize  (cost=0.00..47.05 rows=2470 width=0)
                     ->  Seq Scan on pg_table_a tom0
(cost=0.00..34.70 rows=2470 width=0)
(9 rows)

Filter: ((col_bool IS NOT NULL) AND (col_bool IS NOT NULL))
This makes me unhappy.
Your patch gets the same plan.


-- 
Thanks,
Tender Wang