From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>
Cc: amul sul <sulamul@gmail.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [Patch] ALTER SYSTEM READ ONLY
Date: Wed, 17 Jun 2020 12:27:48 -0400
Message-ID: <1448927.1592411268@sss.pgh.pa.us> (raw)
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Robert Haas <robertmhaas@gmail.com> writes:
> This seems like pretty dubious hand-waving. Of course, things that
> write WAL are going to be broken by a switch that prevents writing
> WAL; but if they were not, there would be no purpose in having such a
> switch, so that's not really an argument. But you seem to have mixed
> in some things that don't require writing WAL, and claimed without
> evidence that those would somehow also be broken.
Which of the things I mentioned don't require writing WAL?
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.
>> I also think that putting such a thing into ALTER SYSTEM has got big
>> logical problems.
> ... no right-thinking person would ever propose to
> change a feature that renders the system read-only in such a way that
> it was impossible to deactivate it. That would be nuts.
My point was that putting this in ALTER SYSTEM paints us into a corner
as to what we can do with ALTER SYSTEM in the future: we won't ever be
able to make that do anything that would require writing WAL. And I
don't entirely believe your argument that that will never be something
we'd want to do.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, robertmhaas@gmail.com, amit.kapila16@gmail.com, sulamul@gmail.com
Subject: Re: [Patch] ALTER SYSTEM READ ONLY
In-Reply-To: <1448927.1592411268@sss.pgh.pa.us>
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