Re: Optimization issue of branching UNION ALL

From: Andrey Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Optimization issue of branching UNION ALL
Date: 2022-12-22 11:59:41
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On 22/12/2022 06:50, Tom Lane wrote:
>> 2. Iterative passes along the append_rel_list for replacing vars in the
>> translated_vars field. I can't grasp real necessity of passing all the
>> append_rel_list during flattening of an union all leaf subquery. No one
>> can reference this leaf, isn't it?
> After thinking about that for awhile, I believe we can go further:
> the containing_appendrel is actually the *only* part of the upper
> query that needs to be adjusted. So we could do something like
> the attached.
> This passes check-world, but I don't have quite enough confidence
> in it to just commit it.
Thanks, I have written the letter because of some doubts too. But only
one weak point I could imagine - if someday sql standard will be changed.
Your code looks better, than previous attempt.

Andrey Lepikhov
Postgres Professional

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