Re: make MaxBackends available in _PG_init

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
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