Re: [Patch] ALTER SYSTEM READ ONLY

Robert Haas <robertmhaas(at)gmail(dot)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