From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Fujii Masao <masao.fujii@oss.nttdata.com>,
        Jehan-Guillaume de Rorthais <jgdr@dalibo.com>,
        PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [patch] demote
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Thu, 18 Jun 2020 13:16:23 -0400"
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Date: Thu, 18 Jun 2020 13:24:38 -0400
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Robert Haas <robertmhaas@gmail.com> writes:
> ... To go back to recovery rather than just to a read-only
> state, I think you'd need to grapple with some additional issues that
> patch doesn't touch, like some of the snapshot-taking stuff, but I
> think you still need to solve all of the problems that it does deal
> with, unless you're OK with killing every session.

It seems like this is the core decision that needs to be taken.  If
we're willing to have these state transitions include a server restart,
then many things get simpler.  If we're not, it's gonna cost us in
code complexity and hence bugs.  Maybe the usability gain is worth it,
or maybe not.

I think it would probably be worth the trouble to pursue both designs in
parallel for awhile, so we can get a better handle on exactly how much
complexity we're buying into with the more ambitious definition.

			regards, tom lane