Re: make MaxBackends available in _PG_init

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Nathan Bossart <nathandbossart(at)gmail(dot)com>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, "Bossart, Nathan" <bossartn(at)amazon(dot)com>, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>, "wangsh(dot)fnst(at)fujitsu(dot)com" <wangsh(dot)fnst(at)fujitsu(dot)com>, Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, Greg Sabino Mullane <htamfids(at)gmail(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: make MaxBackends available in _PG_init
Date: 2022-04-12 20:33:39
Message-ID: 915771.1649795619@sss.pgh.pa.us
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Nathan Bossart <nathandbossart(at)gmail(dot)com> writes:
> On Tue, Apr 12, 2022 at 03:12:42PM -0400, Robert Haas wrote:
>> But if there's even one use case where adjusting GUCs at this phase is
>> reasonable, then 0003 isn't really good enough. We need an 0004 that
>> provides a new hook in a place where such changes can safely be made.

> I think that is doable. IMO it should be ѕomething like _PG_change_GUCs()
> that is called before _PG_init(). The other option is to add a hook called
> after _PG_init() where MaxBackends is available (in which case we likely
> want GetMaxBackends() again). Thoughts?

I like the second option. Calling into a module before we've called its
_PG_init function is just weird, and will cause no end of confusion.

regards, tom lane

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