From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
cc: Amit Kapila <amit.kapila16@gmail.com>, amul sul <sulamul@gmail.com>,
        PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [Patch] ALTER SYSTEM READ ONLY
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Comments: In-reply-to Robert Haas <robertmhaas@gmail.com>
	message dated "Wed, 17 Jun 2020 12:34:53 -0400"
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Date: Wed, 17 Jun 2020 12:45:45 -0400
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Robert Haas <robertmhaas@gmail.com> writes:
> On Wed, Jun 17, 2020 at 12:27 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Which of the things I mentioned don't require writing WAL?

> Writing hint bits and marking index tuples as killed do not write WAL
> unless checksums are enabled.

And your point is?  I thought enabling checksums was considered
good practice these days.

>> You're right that these are the same things that we already forbid on a
>> standby, for the same reason, so maybe it won't be as hard to identify
>> them as I feared.  I wonder whether we should envision this as "demote
>> primary to standby" rather than an independent feature.

> See my comments on the nearby pg_demote thread. I think we want both.

Well, if pg_demote can be done for X amount of effort, and largely
gets the job done, while this requires 10X or 100X the effort and
introduces 10X or 100X as many bugs, I'm not especially convinced
that we want both. 

			regards, tom lane