Re: [PATCH] Extend ALTER OPERATOR to support adding commutator, negator, hashes, and merges

On Tue, Oct 10, 2023 at 9:32 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> 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

Thanks.

I've added another patch (0002-require_unused_neg_com-v1.patch) that
prevents using a commutator or negator that's already part of a pair.
The only other changes from my email yesterday are that in the ALTER
command I moved the post alter hook to after OperatorUpd and the
addition of tests to verify that we can't use an existing commutator
or negator with the ALTER command.

I believe this can all be looked at again.

Cheers,
Tommy