Horton

Re: make MaxBackends available in _PG_init

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Nathan Bossart <nathandbossart@gmail.com>, Andres Freund <andres@anarazel.de>, Julien Rouhaud <rjuju123@gmail.com>, 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>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2022-04-12T21:43:17Z
Lists: pgsql-hackers 
Robert Haas <robertmhaas@gmail.com> writes:
> On Tue, Apr 12, 2022 at 4:58 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> It seems after a bit of reflection that what we ought to do is identify
>> the subset of PGC_POSTMASTER GUCs that feed into shared memory sizing,
>> mark those with a new GUC flag, and not allow them to be changed after
>> shared memory is set up.

> I dunno, I feel like this is over-engineered.

It probably is.  I'm just offering this as a solution if people want to
insist on a mechanism to prevent unsafe GUC changes.  If we drop the
idea of trying to forcibly prevent extensions from Doing It Wrong,
then we don't need this, only the extra hook.

			regards, tom lane

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