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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Robert Haas <robertmhaas@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Cc: Georgios <gkokolatos@protonmail.com>
Subject: Re: index prefetching
Date: Thu, 21 Dec 2023 20:05:52 +0100
Message-ID: <01daded3-edde-9705-d873-d7f7ccaf464e@enterprisedb.com> (raw)
In-Reply-To: <CA+TgmoY5UrCO+NZC6k9NFsiuSrhTFGpYz638he4V_nrrT6=hCA@mail.gmail.com>
References: <6030d836-e8b7-e7b9-2cbb-144309679d03@enterprisedb.com>
	<8c86c3a6-074e-6c88-3e7e-9452b6a37b9b@enterprisedb.com>
	<3cd40425-965a-5ce1-1af3-d51971c44b93@enterprisedb.com>
	<8ec36f51-b863-60e3-20e2-b9c981c5ce5e@enterprisedb.com>
	<06bb7d02-2c44-3062-731e-a735ba13da7e@enterprisedb.com>
	<367160ea-b1ed-4481-e804-bca509128878@enterprisedb.com>
	<cd63c8bc-3d3c-00ab-f7eb-fa55969c3234@enterprisedb.com>
	<20231221132742.kqxt3iujna3z33ab@alap3.anarazel.de>
	<3cfa05ce-d7f2-b2ba-313f-ed0c3c067fc4@enterprisedb.com>
	<CA+TgmoYXvrrcgMXfX=8N-6x4PhdFajzfDXNVizNum-F3pka5Lw@mail.gmail.com>
	<20231221160757.kk2dhl3t3fvbggv5@alap3.anarazel.de>
	<CA+TgmoY5UrCO+NZC6k9NFsiuSrhTFGpYz638he4V_nrrT6=hCA@mail.gmail.com>

On 12/21/23 18:14, Robert Haas wrote:
> On Thu, Dec 21, 2023 at 11:08 AM Andres Freund <andres@anarazel.de> wrote:
>> But I'd like you to feel guilty (no, not really) and fix it (yes, really) :)
> 
> Sadly, you're more likely to get the first one than you are to get the
> second one. I can't really see going back to revisit that decision as
> a basis for somebody else's new work -- it'd be better if the person
> doing the new work figured out what makes sense here.
> 

I think it's a great example of "hindsight is 20/20". There were
perfectly valid reasons to have two separate nodes, and it's not like
these reasons somehow disappeared. It still is a perfectly reasonable
decision.

It's just that allowing index-only filters for regular index scans seems
to eliminate pretty much all executor differences between the two nodes.
But that's hard to predict - I certainly would not have even think about
that back when index-only scans were added.


regards

-- 
Tomas Vondra
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company





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