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From: Andrei Lepikhov <a.lepikhov@postgrespro.ru>
To: Alexander Korotkov <aekorotkov@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Vik Fearing <vik@postgresfriends.org>
Cc: zuming.jiang@inf.ethz.ch, pgsql-bugs@lists.postgresql.org, Alexander Korotkov <akorotkov@postgresql.org>
Subject: Re: BUG #18170: Unexpected error: no relation entry for relid 3
Date: Fri, 27 Oct 2023 16:07:44 +0700
Message-ID: <721542ce-79df-469e-93e9-811fadb5bd0c@postgrespro.ru> (raw)
In-Reply-To: <CAPpHfdsiN0norSHfw3Ujemf=RuPzMxt5PRDiyv0vqUdwSBDtoA@mail.gmail.com>
References: <18170-f1d17bf9a0d58b24@postgresql.org>
	<4ecab120-6be3-4cf6-a2a0-249c73ae91d4@postgresfriends.org>
	<1189851.1698340331@sss.pgh.pa.us>
	<011bcae5-7840-42c7-a50c-b406189e2e78@postgrespro.ru>
	<CAPpHfdsiN0norSHfw3Ujemf=RuPzMxt5PRDiyv0vqUdwSBDtoA@mail.gmail.com>

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






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