Re: BUG #18170: Unexpected error: no relation entry for relid 3

On 27/10/2023 00:12, Tom Lane wrote:
> Vik Fearing <vik(at)postgresfriends(dot)org> writes:
>> On 10/26/23 16:01, PG Bug reporting form wrote:
>>> My fuzzer finds a bug in Postgres, which triggers an unexpected error.
>
>> This bisects to d3d55ce571369dad6e1d582f1655e5a3fbd8594a, Remove useless
>> self-joins.
>
> I wonder if that new code thinks it can remove ref_2 from the query,
> even though ref_2 is used in the targetlist. I'm not seeing
> control reach remove_leftjoinrel_from_query, though.

As I see, this join can be removed: in the explain you can see that
OUTER JOIN is replaced with the INNER JOIN(ref_2, ref_3) ON a key column.
In my opinion, the origin of the problem is that the parent_root
contains a link to ref_2 in its
simple_rte_array[]->subquery->targetList. I am still looking for a
general solution right now, but it doesn't look too complicated at first
sight.

> Also, while nosing around in this, I tried to pprint(root) at the
> point of the error, and got

Yeah, it is my blunder. Alexander already fixed that, as I see. The only
question is whether it is worth making the UniqueRelInfo structure as a
node (for debug purposes - I see only one reason) or we should exclude
this field from read/write operations at all.

--
regards,
Andrei Lepikhov
Postgres Professional