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In-Reply-To: <b0ea6652-d935-420a-ba73-5e9af824176c@vondra.me>
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Thu, 26 Mar 2026 10:51:25 -0400
Message-ID: 
 <CAAKRu_ZCWDHj8d99Biu6n8pvsDNRpiqOQFuZoQZFrnGpiEisog@mail.gmail.com>
Subject: Re: eliminate xl_heap_visible to reduce WAL (and eventually set VM
 on-access)
To: Tomas Vondra <tomas@vondra.me>
Cc: Andres Freund <andres@anarazel.de>,
 Kirill Reshke <reshkekirill@gmail.com>,
	Chao Li <li.evan.chao@gmail.com>, Andrey Borodin <x4mmm@yandex-team.ru>,
	Xuneng Zhou <xunengzhou@gmail.com>, Robert Haas <robertmhaas@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Heikki Linnakangas <hlinnaka@iki.fi>
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On Wed, Mar 25, 2026 at 7:29=E2=80=AFPM Tomas Vondra <tomas@vondra.me> wrot=
e:
>
> >> - Do we really want to pass two sets of flags to table_beginscan_commo=
n?
> >>  I realize it's done to ensure "users" don't use internal flags, but
> >> then maybe it'd be better to do that check in the places calling the
> >> _common? Someone adding a new caller can break this in various ways
> >> anyway, e.g. by setting bits in the internal flags, no?
> >
> > Yes, callers of table_beginscan_common() could pass flags they
> > shouldn't in internal_flags. But I was mostly trying to prevent the
> > case where a user picks a flag that overlaps with an internal flag,
> > conditionally passes it as a user flag, and then when they test for it
> > in their AM-specific code, they aren't actually checking if their own
> > flag is set.
>
> Ah, so we expect people to invent their "own" flags, outside what's in
> ScanOptions? Or do I misunderstand how it works? (I admit not reading
> the whole massive thread, as I was only interested in using the flags in
> my own patch.)

Yes, this isn't really explored in the rest of the thread. I thought
since the flags are threaded all the way through and they can
set/check the flags in the table AM-specific layer, it would make
sense that they could choose flags for their own purposes. They don't
have to wait for consensus on getting a new SO type added. I don't
know if this is a bad idea. However, changing the table AM wrappers
seems more justifiable if we are making them extensible in this way.

> >> If we want to have these checks, should we be more thorough? Should we
> >> check the internal flags only set internal flags?
> >
> > That's easy enough too.
> > Assert((internal_flags & ~SO_INTERNAL_FLAGS) =3D=3D 0); I think does th=
e trick.

I did this in the previously posted v46.

- Melanie