Andrei Lepikhov <lepihov@gmail.com> 于2026年3月27日周五 03:59写道：
>
> On 20/3/26 15:02, Alexander Korotkov wrote:
> > OK. I've pushed this. Let's go back to
> > restrict_infos_logically_equal(). I'm still not convinced that we
> > need to check if required_relids is singleton. Why we can ignore
> > outer_relids for singleton, but can't do if, for instance, two
> > relations involved?
>
> Let's continue. In the attachment, the Tender's proposal that I changed
> a little and added some tests.
>
> As you can see in the tests, the SINGLETON limitation keeps duplicates
> of clauses like 'a.x + b.y = c'.
> This example shows the main flaw of this approach. Introducing the
> restrict_infos_logically_equal(), we do a little more job than just the
> equal() routine could because of the context where we call this function
> and on which clauses.
> But skipping all other RestrictInfo fields except required_relids seems
> excessive. - see the example with security_level difference - ignoring
> its value, we potentially might remove the clause with enforced security
> level in favour of an unsecured one.
Yes, it seems too strict to require all fields to be equal, but
skipping some fields is unsafe.
> That's more, further some new optimisations might introduce more fields
> into RestrictInfo that should be checked to correctly decide on the
> equality, and we may forget to arrange this specific place.
>
Agree.
> So, formally it works, and making the following replacement, we close
> the singleton issue:
>
> - if (bms_membership(a->required_relids) == BMS_SINGLETON &&
> - a->security_level == b->security_level)
> + if (bms_equal(a->required_relids, b->required_relids) &&
> + a->security_level == b->security_level &&
> + a->is_pushed_down == b->is_pushed_down)
>
The singleton issue does not seem to be the correct way; I don't dive
deeply to cover all cases.
> but I'm unsure, in general, that this approach is conservative enough.
> Maybe we shouldn’t change this logic and invent one more optimisation
> ‘deduplication’ stage later, before the selectivity estimation stage.
--
Thanks,
Tender Wang
