Horton

Re: make MaxBackends available in _PG_init

Julien Rouhaud <rjuju123@gmail.com>

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From: Julien Rouhaud <rjuju123@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Nathan Bossart <nathandbossart@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: 2022-04-11T15:36:31Z
Lists: pgsql-hackers 
Hi,

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:
>
> > On the bright side, I see that citus is using SetConfigOption() to increase
> > max_prepared_transactions [1].  That's the only extension mentioned in that
> > thread that does modify some GUC, and this GUC was already marked as
> > PGDLLIMPORT since 2017 so it probably wasn't done that way for Windows
> > compatibility reason.
>
> I don't quite understand this, but I think if we want to support this
> kind of thing it needs a separate hook.

My point was that even if we say we don't support this, we have no way to
actually fully enforce it, as the variables are exported.  So it's good that
the only know case is using the GUC API, since we can enforce this one.

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