Re: Schema variables - new implementation for Postgres 15 (typo)

From: Dmitry Dolgov <9erthalion6(at)gmail(dot)com>
To: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Cc: Erik Rijkers <er(at)xs4all(dot)nl>, Sergey Shinderuk <s(dot)shinderuk(at)postgrespro(dot)ru>, Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, dean(dot)a(dot)rasheed(at)gmail(dot)com, joel(at)compiler(dot)org, pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: Schema variables - new implementation for Postgres 15 (typo)
Date: 2022-12-22 21:23:52
Message-ID: 20221222212352.cs62srlidjxgcjdp@ddolgov.remote.csb
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> On Thu, Dec 22, 2022 at 08:45:57PM +0100, Pavel Stehule wrote:
> > From the first look it seems some major topics the discussion is evolving
> > are about:
> >
> > * Validity of the use case. Seems to be quite convincingly addressed in
> > [1] and
> > [2].
> >
> > * Complicated logic around invalidation, concurrent create/drop etc. (I
> > guess
> > the issue above is falling into the same category).
> >
> > * Concerns that session variables could repeat some problems of temporary
> > tables.
> >
>
> Why do you think so? The variable has no mvcc support - it is just stored
> value with local visibility without mvcc support. There can be little bit
> similar issues like with global temporary tables.

Yeah, sorry for not being precise, I mean global temporary tables. This
is not my analysis, I've simply picked up it was mentioned a couple of
times here. The points above are not meant to serve as an objection
against the patch, but rather to figure out if there are any gaps left
to address and come up with some sort of plan with "committed" as a
final destination.

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