Re: warning to publication created and wal_level is not set to logical

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: David Fetter <david(at)fetter(dot)org>
Cc: Lucas Viecelli <lviecelli199(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: warning to publication created and wal_level is not set to logical
Date: 2019-03-24 18:06:59
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David Fetter <david(at)fetter(dot)org> writes:
> On Thu, Mar 21, 2019 at 07:45:59PM -0300, Lucas Viecelli wrote:
>> I am sending a patch that when an PUBLICATION is created and the
>> wal_level is different from logical prints a WARNING in console/log:

> Is a WARNING sufficient? Maybe I'm misunderstanding something
> important, but I think the attempt should fail with a HINT to set the
> wal_level ahead of time.

That would be a booby-trap for dump/restore and pg_upgrade, so I don't
think making CREATE PUBLICATION fail outright would be wise.

> Possibly in a separate patch, setting the wal_level to anything lower
> than logical when publications exist should also fail.

I do not believe this is practical either. GUC manipulation cannot
look at the catalogs.

I agree that it'd be nice to be noisier about the problem, but I'm
not sure we can do more than bleat in the postmaster log from time
to time if a publication is active and wal_level is too low.
(And we'd better be careful about the log-spam aspect of that...)

regards, tom lane

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