MIME-Version: 1.0
References: 
 <CA+HiwqFpZ80UJKr4tZus4Omgg7YESzFXKSwSHRW2Ap2=XSVyUA@mail.gmail.com>
 <54c35fb9-da3a-4754-ab8c-46ed0b612465@vondra.me>
 <CA+HiwqH8N-SxEB6SysEBsYNgV_KJs66k9Z2SNmqVzbBP-60yWg@mail.gmail.com>
 <684c70d7-180e-461d-9377-600c2db581ba@vondra.me>
 <CA+HiwqEmG9YCQvG6uux7sO=jKFSAW6hA4Ea-ymfD+JhJAe4PWQ@mail.gmail.com>
 <CA+HiwqE2FfJfH=siLiR3kJ13tmXZORAGTWsZc2r52o1_5BDv+g@mail.gmail.com>
 <bfcc1b78-aa39-4356-8f42-b8cfb9733d6e@vondra.me>
 <CA+HiwqFhkpXHAA=4NY5SqYXX08uq=nYtXcSByNZF=2MAy1UA7A@mail.gmail.com>
 <CA+HiwqHCcSoYfpMjFshaU1bj6NjreiDvMSDpVSeBmqk-kbWrPw@mail.gmail.com>
 <CA+HiwqHOejJk0_qMuM5g38h70hY_JvHMAKwnH3k=urfTXauPQA@mail.gmail.com>
 <CA+HiwqFsGKM82oaMby3VWYXf_XFpDAMeT+6SXgj-45HpTrS1dA@mail.gmail.com>
 <CA+HiwqFA5hUWYktt3VMh4zQOYMxqH-MpdX8eemfM+o-9dY-zbQ@mail.gmail.com>
 <CA+HiwqEn7bbUXaXO=SmUujBjJSHfS31cwQroHRBwT0sR=66bgg@mail.gmail.com>
 <CA+HiwqGGLDTd1ZTK1c0zv4La7XOVSVMqBuNtscJeh6FyUQvFvA@mail.gmail.com>
 <CA+HiwqE2JFiqqrXdyJVQWY-fMGwzDkLqjXQdUKbPaCpDpxd_2g@mail.gmail.com>
 <CA+HiwqFp3jZGSz==QjeuV62_62F6+V6b62=Uqvy99sW_gsgWBA@mail.gmail.com>
 <CAHewXNkUz9XGG8nnoxZaw35e+5bQVVP=eeJE4cW4V2e+P9ndFw@mail.gmail.com>
 <CA+HiwqFKSpfYruzcVz-5CcFxg7gMa+ycXjMa2aPz_J_P4LGXTg@mail.gmail.com>
 <605328.1747710381@sss.pgh.pa.us>
 <CA+HiwqEQ1oME-hcDXwC9rGQb=u7MdUFG3Sc=Qg27uH480v10FA@mail.gmail.com>
 <691261.1747755511@sss.pgh.pa.us>
In-Reply-To: <691261.1747755511@sss.pgh.pa.us>
From: Robert Haas <robertmhaas@gmail.com>
Date: Thu, 22 May 2025 09:50:22 -0400
Message-ID: 
 <CA+TgmoYbka16N95km-7wFtPk3CzTO2g0dGssXex1ygvb0g+miw@mail.gmail.com>
Subject: Re: generic plans and "initial" pruning
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Amit Langote <amitlangote09@gmail.com>, Tender Wang <tndrwang@gmail.com>,
	Alexander Lakhin <exclusion@gmail.com>, Tomas Vondra <tomas@vondra.me>,
	Alvaro Herrera <alvherre@alvh.no-ip.org>, Andres Freund <andres@anarazel.de>,
	Daniel Gustafsson <daniel@yesql.se>, David Rowley <dgrowleyml@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@postgresql.org>,
 Thom Brown <thom@linux.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Archived-At: 
 <https://www.postgresql.org/message-id/CA%2BTgmoYbka16N95km-7wFtPk3CzTO2g0dGssXex1ygvb0g%2Bmiw%40mail.gmail.com>
Precedence: bulk

On Tue, May 20, 2025 at 11:38=E2=80=AFAM Tom Lane <tgl@sss.pgh.pa.us> wrote=
:
> I still like the core idea of deferring locking, but I don't like
> anything about this implementation of it.  It seems like there has
> to be a better and simpler way.

Without particularly defending this implementation, and certainly
without defending its bugs, I just want to say that I'm not convinced
by the idea that there has to be a better and simpler way. We --
principally Amit, but also me and you and others -- have been trying
to find the best way of doing this for probably 5 years now. If you do
something during executor startup, you have to be prepared for
executor startup to force a replan, and if you do something before
executor startup, then you're duplicating executor logic into a new
phase that needs to communicate its results forward to execution
proper. Either approach is awkward and that awkwardness seems to
inevitably bleed into the plan cache specifically. I'd be beyond
delighted if you want to help chart a path through the awkwardness
here, since you know this stuff better than anybody, but I am
skeptical that there is a truly marvelous approach which we've just
managed to overlook for all this time.

--=20
Robert Haas
EDB: http://www.enterprisedb.com