On 27/10/2023 15:17, Alexander Korotkov wrote:
> On Fri, Oct 27, 2023 at 9:31 AM Andrei Lepikhov
> <a.lepikhov@postgrespro.ru> wrote:
>> On 27/10/2023 00:12, Tom Lane wrote:
>>> Vik Fearing <vik@postgresfriends.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.
>
> Yes, I came to the same conclusion. We process root->parse. But I
> didn't get why parent_root->simple_rte_array[]->subquery is not the
> same as root->parse. They look the same, but they are distinct
> copies. If they were the same pointers, there would be no problem.
As I see, the copy of the parse tree is induced by the same feature as
usual in the last few months: 2489d76. It introduced
remove_nulling_relids, and it altered our parse tree. Right now, I don't
have an answer: it should be fixed in SJE, or this is a more general
issue just discovered by the SJE.
--
regards,
Andrei Lepikhov
Postgres Professional
