| From: | "David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Jakub Wartak <jakub(dot)wartak(at)enterprisedb(dot)com>, Alexandra Wang <alexandra(dot)wang(dot)oss(at)gmail(dot)com>, Richard Guo <guofenglinux(at)gmail(dot)com>, Lukas Fittl <lukas(at)fittl(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Jacob Champion <jacob(dot)champion(at)enterprisedb(dot)com>, Dian Fay <di(at)nmfay(dot)com>, Matheus Alcantara <matheusssilv97(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: pg_plan_advice (now with transparent SQL plan performance overrides - pg_stash_advice) |
| Date: | 2026-03-04 04:11:38 |
| Message-ID: | CAKFQuwaA09Kxfbv2tgh-SaaCXLD5+grYj3F9RNGQhTHsXz9ENw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Tuesday, March 3, 2026, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> >
> > SEQ_SCAN(t1(at)minmax_1) /* matched, failed */
>
> Because there's not a way to control aggregation behavior at present,
> you can't directly conrol whether t1 or t1(at)minmax_1 appears in the
> winning plan.
Ok, that’s what I was missing here, it saw the subplan in its options but
the winning plan didn’t include it. So “matched/failed” may produce a plan
where the target having been matched isn’t actually visible to the user.
Maybe add a note like this to pg_plan_advice:
Generated advice is produced to a high level of specificity without knowing
what limitations the advice interpreter has in applying that advice.
Therefore, generated advice targets may later fail for no other reason than
cost-based decisions resulted in the originally chosen plan to no longer be
chosen. The planner will still likely see the original target on a now
losing plan and thus the advice feedback will report matched even when the
winning plan does not include the specific target.
David J.
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