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

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Vik Fearing <vik(at)postgresfriends(dot)org>
Cc: zuming(dot)jiang(at)inf(dot)ethz(dot)ch, pgsql-bugs(at)lists(dot)postgresql(dot)org, Alexander Korotkov <akorotkov(at)postgresql(dot)org>
Subject: Re: BUG #18170: Unexpected error: no relation entry for relid 3
Date: 2023-10-26 17:12:11
Message-ID: 1189851.1698340331@sss.pgh.pa.us
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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.

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

2023-10-26 12:48:37.852 EDT [1186007] WARNING: could not dump unrecognized node type: 37413808

This happens because the patch changed RelOptInfo.unique_for_rels from
a list of Bitmapsets into a list of UniqueRelInfo, even though it did
not bother to make UniqueRelInfo be a Node type (much less document
the change in globally-visible data structures: pathnodes.h still says
it's a list of Relid sets). This is not acceptable.

I'm getting the distinct impression that this patch wasn't
ready for prime time.

regards, tom lane

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