From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tommy Pavlicek <tommypav122@gmail.com>
cc: =?UTF-8?Q?Dagfinn_Ilmari_Manns=C3=A5ker?= <ilmari@ilmari.org>,
        pgsql-hackers@lists.postgresql.org,
        Tomas Vondra <tomas.vondra@enterprisedb.com>,
        jian.universality@gmail.com
Subject: Re: [PATCH] Extend ALTER OPERATOR to support adding commutator,
 negator, hashes, and merges
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Comments: In-reply-to Tommy Pavlicek <tommypav122@gmail.com>
	message dated "Tue, 10 Oct 2023 21:12:50 +0100"
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Date: Tue, 10 Oct 2023 16:32:07 -0400
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Tommy Pavlicek <tommypav122@gmail.com> writes:
> I did notice one further potential bug. When creating an operator and
> adding a commutator, PostgreSQL only links the commutator back to the
> operator if the commutator has no commutator of its own, but the
> create operation succeeds regardless of whether this linkage happens.

> In other words, if A and B are a pair of commutators and one creates
> another operator, C, with A as its commutator, then C will link to A,
> but A will still link to B (and B to A). It's not clear to me if this
> in itself is a problem, but unless I've misunderstood something
> operator C must be the same as B so it implies an error by the user
> and there could also be issues if A was deleted since C would continue
> to refer to the deleted A.

Yeah, it'd make sense to tighten that up.  Per the discussion so far,
we should not allow an operator's commutator/negator links to change
once set, so overwriting the existing link with a different value
would be wrong.  But allowing creation of the new operator to proceed
with a different outcome than expected isn't good either.  I think
we should start throwing an error for that.

			regards, tom lane