Re: archive modules

On Wed, Sep 14, 2022 at 06:12:09PM -0400, Tom Lane wrote:
> Nathan Bossart <nathandbossart@gmail.com> writes:
>> On Wed, Sep 14, 2022 at 04:47:23PM -0400, Tom Lane wrote:
>>> Yeah, the objection there is only to trying to enforce such
>>> interrelationships in GUC hooks.  In this case it seems to me that
>>> we could easily check and complain at the point where we're about
>>> to use the GUC values.
> 
>> I think the cleanest way to do something like that would be to load a
>> check_configured_cb that produces a WARNING.  IIRC failing in
>> LoadArchiveLibrary() would just cause the archiver process to restart over
>> and over.  HandlePgArchInterrupts() might need some work as well.
> 
> Hm.  Maybe consistency-check these settings in the postmaster, sometime
> after we've absorbed all GUC settings but before we launch any children?
> That could provide a saner implementation for the recovery_target_*
> variables too.

Both archive_command and archive_library are PGC_SIGHUP, so IIUC that
wouldn't be sufficient.  I attached a quick sketch that seems to provide
the desired behavior.  It's nowhere near committable yet, but it
demonstrates what I'm thinking.

For recovery_target_*, something like you are describing seems reasonable.
I believe PostmasterMain() already performs some similar checks.

-- 
Nathan Bossart
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