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From: Tom Lane <[email protected]>
To: Robert Haas <[email protected]>
Cc: Nathan Bossart <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: Julien Rouhaud <[email protected]>
Cc: Michael Paquier <[email protected]>
Cc: Bossart, Nathan <[email protected]>
Cc: Fujii Masao <[email protected]>
Cc: [email protected] <[email protected]>
Cc: Bharath Rupireddy <[email protected]>
Cc: Greg Sabino Mullane <[email protected]>
Cc: [email protected] <[email protected]>
Subject: Re: make MaxBackends available in _PG_init
Date: Tue, 12 Apr 2022 15:21:57 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <CA+TgmoY4og1VADa78VySwsTjtTQbtXbnRPSq9x=e6ogS_wWfaw@mail.gmail.com>
References: <[email protected]>
	<CA+Tgmoawc-4i3uFkNdwp8wUR9-jmfV0xjKDyJvGR9t2k2f=1EQ@mail.gmail.com>
	<20220330163051.GA784643@nathanxps13>
	<YlGJGiofZiWN3elx@jrouhaud>
	<CA+TgmoZRnwF=9tMX0TiqZGC4qAK_27NweKd5r-S=OSaE_nL70A@mail.gmail.com>
	<20220411164408.GA1915258@nathanxps13>
	<CA+TgmoZVQznhWpUr-bjC9U=Won8ZnfozSkiXrW2HU80r6QyASQ@mail.gmail.com>
	<20220411204442.GA2004824@nathanxps13>
	<20220411211435.GA2057981@nathanxps13>
	<[email protected]>
	<20220412180306.GA2063516@nathanxps13>
	<CA+TgmoY4og1VADa78VySwsTjtTQbtXbnRPSq9x=e6ogS_wWfaw@mail.gmail.com>

Robert Haas <[email protected]> writes:
> Gah, I hate putting this off for another year, but I guess I'm also
> not convinced that 0003 has the right idea, so maybe it's for the
> best. Here's what's bugging me: 0003 decrees that _PG_init() is the
> Wrong Place to Adjust GUC Settings. Now, that begs the question: what
> is the right place to adjust GUC settings? I argued upthread that
> extensions shouldn't be overriding values from postgresql.conf at all,
> but on further reflection I think there's at least one legitimate use
> case for this sort of thing: some kind of auto-tuning module that, for
> example, looks at how much memory you have and sets shared_buffers or
> work_mem or something based on the result.

Yeah.  It's a very long way from "changing shared memory sizes here
doesn't work" to "no extension is allowed to change any GUC at load
time".  A counterexample is that it's not clear why an extension
shouldn't be allowed to define a GUC using DefineCustomXXXVariable
and then immediately set it to some other value.  I think trying to
forbid that across-the-board is going to mostly result in breaking
a lot of cases that are perfectly safe.

			regards, tom lane






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