Date: Wed, 11 Nov 2020 14:18:04 -0800
From: Andres Freund <andres@anarazel.de>
To: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: sfrost@snowman.net, osumi.takamichi@fujitsu.com,
	masao.fujii@oss.nttdata.com, ashutosh.bapat.oss@gmail.com,
	tsunakawa.takay@fujitsu.com, pgsql-hackers@lists.postgresql.org
Subject: Re: In-placre persistance change of a relation
Message-ID: <20201111221804.cs3kbhypjmui2aiy@alap3.anarazel.de>
References: <20201111.173317.460890039962481381.horikyota.ntt@gmail.com>
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Hi,

I suggest outlining what you are trying to achieve here. Starting a new
thread and expecting people to dig through another thread to infer what
you are actually trying to achive isn't great.

FWIW, I'm *extremely* doubtful it's worth adding features that depend on
a PGC_POSTMASTER wal_level=minimal being used. Which this does, a far as
I understand.  If somebody added support for dynamically adapting
wal_level (e.g. wal_level=auto, that increases wal_level to
replica/logical depending on the presence of replication slots), it'd
perhaps be different.


On 2020-11-11 17:33:17 +0900, Kyotaro Horiguchi wrote:
> FWIW this is a revised version of the PoC, which has some known
> problems.
> 
> - Flipping of Buffer persistence is not WAL-logged nor even be able to
>   be safely roll-backed. (It might be better to drop buffers).

That's obviously a no-go. I think you might be able to address this if
you accept that the command cannot be run in a transaction (like
CONCURRENTLY). Then you can first do the catalog changes, change the
persistence level, and commit.

Greetings,

Andres Freund