Horton

Re: make MaxBackends available in _PG_init

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Julien Rouhaud <rjuju123@gmail.com>, Andres Freund <andres@anarazel.de>, Michael Paquier <michael@paquier.xyz>, "Bossart, Nathan" <bossartn@amazon.com>, Fujii Masao <masao.fujii@oss.nttdata.com>, "wangsh.fnst@fujitsu.com" <wangsh.fnst@fujitsu.com>, 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>
Date: 2022-04-11T16:44:08Z
Lists: pgsql-hackers

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On Mon, Apr 11, 2022 at 10:47:17AM -0400, Robert Haas wrote:
> On Sat, Apr 9, 2022 at 9:24 AM Julien Rouhaud <rjuju123@gmail.com> wrote:
>> > FWIW I would be on board with reverting all the GetMaxBackends() stuff if
>> > we made the value available in _PG_init() and stopped supporting GUC
>> > overrides by extensions (e.g., ERROR-ing in SetConfigOption() when
>> > process_shared_preload_libraries_in_progress is true).
>>
>> Yeah I would prefer this approach too, although it couldn't prevent extension
>> from directly modifying the underlying variables so I don't know how effective
>> it would be.
> 
> I think I also prefer this approach. I am willing to be convinced
> that's the wrong idea, but right now I favor it.

Here are some patches.  0001 reverts all the recent commits in this area,
0002 is the patch I posted in August, and 0003 is an attempt at blocking
GUC changes in preloaded libraries' _PG_init() functions.

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

Commits

  1. Add a new shmem_request_hook hook.

  2. Remove non-functional code for unloading loadable modules.

  3. Fix misleading comments about background worker registration.

  4. Revert the addition of GetMaxBackends() and related stuff.

  5. Fix typo in multixact.c

  6. Reduce more the number of calls to GetMaxBackends()

  7. Remove MaxBackends variable in favor of GetMaxBackends() function.

  8. Fix comments about bgworker registration before MaxBackends initialization

  9. Fix bogus assertion in BootstrapModeMain().

  10. Make sure MaxBackends is always set