Re: CUBE seems a bit confused about ORDER BY

On 12/12/2017 01:52 PM, Alexander Korotkov wrote:
> On Tue, Dec 12, 2017 at 3:49 PM, Teodor Sigaev <teodor(at)sigaev(dot)ru
> <mailto:teodor(at)sigaev(dot)ru>> wrote:
>
> Yes, the thing is that we change behavior of existing ~>
> operator.  In general, this is not good idea because it could
> affect existing users whose already use this operator. 
> Typically in such situation, we could leave existing operator as
> is, and invent new operator with new behavior.  However, in this
> particular case, I think there are reasons to make an exception
> to the rules.  The reasons are following:
> 1) The ~> operator was designed especially for knn gist.
> 2) Knn gist support for current behavior is broken by design and
> can't be fixed.  Most we can do to fix existing ~> operator
> behavior as is to drop knn gist support.  But then ~> operator
> would be left useless.
> 3) It doesn't seems that ~> operator have many users yet,
> because an error wasn't reported during whole release cycle.
>
> I hope these reasons justify altering behavior of existing
> operator as an exception to the rules.  Another question is
> whether we should backpatch it.  But I think we could leave this
> decision to committer.
>
>     I think that this patch is ready for committer.
>
> I'm agree with changing behavior of existing ~> operator, but is any
> objection here? Current implementation is not fixable and I hope
> that users which use this operator will understand why we change it.
> Fortunately, the fix doesn't require changes in system catalog.
>
> The single question here is about index over expression with this
> operator, they will need to reindex, which should be noted in
> release notes.
>
>
> Yes.  I bet only few users have built indexes over ~> operator if any. 
> Ask them to reindex in the release notes seems OK for me.
>

Is there a good way to detect such cases? Either in pg_upgrade, so that
we can print warnings, or at least manually (which would be suitable for
release notes).

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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