Re: Add a GUC check hook to ensure summarize_wal cannot be enabled when wal_level is minimal

On 2024/07/11 0:44, Nathan Bossart wrote:
> On Wed, Jul 10, 2024 at 11:11:13AM -0400, Tom Lane wrote:
>> Please, no. We went through a ton of permutations of that kind of
>> idea years ago, when it first became totally clear that cross-checks
>> between GUCs do not work nicely if implemented in check_hooks.
>> (You can find all the things we tried in the commit log, although
>> I don't recall exactly when.)
>
> Understood.
>
>> A counter-example for what you just
>> said is when a configuration file like the above is loaded after
>> postmaster start.
>
> I haven't tested it, but from skimming around the code, it looks like
> ProcessConfigFileInternal() would deduplicate any previous entries in the
> file prior to applying the values and running the check hooks. Else,
> reloading a configuration file with multiple startup-only GUC entries could
> fail, even without bogus GUC check hooks.

Yeah, I'm thinking the same.

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION