Re: Optimization issue of branching UNION ALL - Mailing list pgsql-hackers

From Richard Guo
Subject Re: Optimization issue of branching UNION ALL
Date
Msg-id CAMbWs49fj701dxtmo9A7e+Bu_aR1xyLNPL4dPG+W0cT43QKgyg@mail.gmail.com
Whole thread Raw
In response to Re: Optimization issue of branching UNION ALL  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: Optimization issue of branching UNION ALL
List pgsql-hackers

On Thu, Dec 22, 2022 at 9:50 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
Andrey Lepikhov <a.lepikhov@postgrespro.ru> writes:
> Superficial study revealed possibly unnecessary operations that could be
> avoided:
> 1. Walking across a query by calling substitute_phv_relids() even if
> lastPHId shows that no one phv is presented.

Yeah, we could do that, and it'd help some.
 
I noticed we also check 'parse->hasSubLinks' when we fix PHVs and
AppendRelInfos in pull_up_simple_subquery.  I'm not sure why we have
this check.  It seems not necessary.

In remove_result_refs, I don't think we need to check 'lastPHId' again
before calling substitute_phv_relids, since it has been checked a few
lines earlier.

Thanks
Richard

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