Date: Fri, 28 Jan 2022 20:33:42 -0800
From: Nathan Bossart <nathandbossart@gmail.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: "Bossart, Nathan" <bossartn@amazon.com>,
	Robert Haas <robertmhaas@gmail.com>,
	Fujii Masao <masao.fujii@oss.nttdata.com>,
	"wangsh.fnst@fujitsu.com" <wangsh.fnst@fujitsu.com>,
	Andres Freund <andres@anarazel.de>,
	Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>,
	Greg Sabino Mullane <htamfids@gmail.com>,
	Tom Lane <tgl@sss.pgh.pa.us>,
	"pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Subject: Re: make MaxBackends available in _PG_init
Message-ID: <20220129043342.GA89174@nathanxps13>
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On Sat, Jan 29, 2022 at 11:19:12AM +0900, Michael Paquier wrote:
> On Thu, Jan 27, 2022 at 10:18:15AM -0800, Nathan Bossart wrote:
>> Alright.  I think the comment adjustments still apply, so I split those out
>> to a new patch.
> 
> Looks fine after a second look, so applied.

Thanks!

> As of the issues of this thread, we really have two things to think
> about:
> 1) How do we want to control the access of some parameters in a
> context or another?  One idea would be more control through GUCs, say
> with a set of context-related flags that prevent the read of some
> variables until they are set.  We could encourage the use of
> GetConfigOption() for that.  For MaxBackends, we could add a read-only
> GUC for this purpose.  That's what Andres hinted at upthread, I
> guess.
> 2) How do we deal with unwanted access of shared parameters?  This one
> is not really controllable, is it?  And we are talking about much more
> than MaxBackends.  This could perhaps be addressed with more
> documentation in the headers for the concerned variables, as a first
> step.

Hm.  Perhaps we should understand the full scope of the problem first.
What else besides MaxBackends and the shared memory GUCs won't be properly
initialized when the shared_preload_libraries' _PG_init() functions are
called?  MaxBackends seems to be the only one that folks have experienced
problems with, which is why I initially zeroed in on it.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com