On Tue, Apr 9, 2024 at 8:55 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Andrei Lepikhov <a.lepikhov@postgrespro.ru> writes:
> > On 9/4/2024 09:12, Tom Lane wrote:
> >> I have another one that I'm not terribly happy about:
> >> Author: Alexander Korotkov <akorotkov@postgresql.org>
> >> Branch: master [72bd38cc9] 2024-04-08 01:27:52 +0300
> >> Transform OR clauses to ANY expression
>
> >> * What the medical community would call off-label usage of
> >> query jumbling. I'm not sure this is even correct as-used,
> >> and for sure it's using that code for something never intended.
> >> Nor is the added code adequately (as in, at all) documented.
>
> > I agree with documentation and disagree with critics on the expression
> > jumbling. It was introduced in the core. Why don't we allow it to be
> > used to speed up machinery with some hashing?
>
> I would back up from that a good deal: why do we need to hash here in
> the first place? There's no evidence I'm aware of that it's needful
> from a performance standpoint.
I think the feature is aimed to deal with large OR lists. I've seen a
significant degradation on 10000 or-clause-groups. That might seem
like awfully a lot, but actually it's not unachievable in generated
queries.
Links.
1. https://www.postgresql.org/message-id/CAPpHfduJtO0s9E%3DSHUTzrCD88BH0eik0UNog1_q3XBF2wLmH6g%40mail.gmail.com
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Regards,
Alexander Korotkov