From: Tom Lane <tgl@sss.pgh.pa.us>
To: Nathan Bossart <nathandbossart@gmail.com>
cc: Fujii Masao <masao.fujii@oss.nttdata.com>,
        pgsql-hackers@lists.postgresql.org
Subject: Re: Add a GUC check hook to ensure summarize_wal cannot be enabled
 when wal_level is minimal
In-reply-to: <ZoVgXuYWbzTLXyRY@nathan>
References: <6e30082e-041b-4e31-9633-95a66de76f5d@oss.nttdata.com>
 <ZoVgXuYWbzTLXyRY@nathan>
Comments: In-reply-to Nathan Bossart <nathandbossart@gmail.com>
	message dated "Wed, 03 Jul 2024 09:29:50 -0500"
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Date: Wed, 03 Jul 2024 11:16:42 -0400
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Nathan Bossart <nathandbossart@gmail.com> writes:
> This sort of thing comes up enough that perhaps we should add a
> better-supported way to deal with GUCs that depend on each other...

Yeah, a GUC check hook that tries to inspect the value of some
other GUC is generally going to create more problems than it
solves; we've learned that the hard way in the past.  We have
your patch to remove one instance of that on the CF queue:

https://www.postgresql.org/message-id/flat/ZnMr2k-Nk5vj7T7H@nathan

But that fix only works because those GUCs are PGC_POSTMASTER
and so we can perform a consistency check on them after GUC setup.

I'm not sure what a more general consistency check mechanism would
look like, but it would have to act at some other point than the
check_hooks do.

			regards, tom lane