On 12/3/2024 22:20, Alexander Korotkov wrote:
> On Mon, Mar 11, 2024 at 2:43 PM Andrei Lepikhov
>> I think you are right. It is probably a better place than any other to
>> remove duplicates in an array. I just think we should sort and remove
>> duplicates from entry->consts in one pass. Thus, this optimisation
>> should be applied to sortable constants.
>
> Ok.
New version of the patch set implemented all we have agreed on for now.
We can return MAX_SAOP_ARRAY_SIZE constraint and Alena's approach to
duplicates deletion for non-sortable cases at the end.
>
>> Hmm, we already tried to do it at that point. I vaguely recall some
>> issues caused by this approach. Anyway, it should be done as quickly as
>> possible to increase the effect of the optimization.
>
> I think there were provided quite strong reasons why this shouldn't be
> implemented at the parse analysis stage [1], [2], [3]. The
> canonicalize_qual() looks quite appropriate place for that since it
> does similar transformations.
Ok. Let's discuss these reasons. In Robert's opinion [1,3], we should do
the transformation based on the cost model. But in the canonicalize_qual
routine, we still make the transformation blindly. Moreover, the second
patch reduces the weight of this reason, doesn't it? Maybe we shouldn't
think about that as about optimisation but some 'general form of
expression'?
Peter [2] worries about the possible transformation outcomes at this
stage. But remember, we already transform clauses like ROW() IN (...) to
a series of ORs here, so it is not an issue. Am I wrong?
Why did we discard the attempt with canonicalize_qual on the previous
iteration? - The stage of parsing is much more native for building SAOP
quals. We can reuse make_scalar_array_op and other stuff, for example.
During the optimisation stage, the only list partitioning machinery
creates SAOP based on a list of constants. So, in theory, it is possible
to implement. But do we really need to make the code more complex?
>
> Links.
> 1. https://www.postgresql.org/message-id/CA%2BTgmoZCgP6FrBQEusn4yaWm02XU8OPeoEMk91q7PRBgwaAkFw%40mail.gmail.com
> 2. https://www.postgresql.org/message-id/CAH2-Wzm2%3Dnf_JhiM3A2yetxRs8Nd2NuN3JqH%3Dfm_YWYd1oYoPg%40mail.gmail.com
> 3. https://www.postgresql.org/message-id/CA%2BTgmoaOiwMXBBTYknczepoZzKTp-Zgk5ss1%2BCuVQE-eFTqBmA%40mail.gmail.com
--
regards,
Andrei Lepikhov
Postgres Professional