Horton

Re: make MaxBackends available in _PG_init

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: Julien Rouhaud <rjuju123@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Nathan Bossart <nathandbossart@gmail.com>, "Bossart, Nathan" <bossartn@amazon.com>, Fujii Masao <masao.fujii@oss.nttdata.com>, "wangsh.fnst@fujitsu.com" <wangsh.fnst@fujitsu.com>, Andres Freund <andres@anarazel.de>, 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: 2022-03-25T05:08:09Z
Lists: pgsql-hackers 
On Fri, Mar 25, 2022 at 11:11:46AM +0800, Julien Rouhaud wrote:
> As an example, here's a POC for a new shmem_request_hook hook after _PG_init().
> With it I could easily fix pg_wait_sampling shmem allocation (and checked that
> it's indeed requesting the correct size).

Are you sure that the end of a release cycle is the good moment to
begin designing new hooks?  Anything added is something we are going
to need supporting moving forward.  My brain is telling me that we
ought to revisit the business with GetMaxBackends() properly instead,
and perhaps revert that.

This solution makes me uneasy from the start (already stated
upthread), because it is not a solution to the original problem, just
a safeguard that handles one small-ish portion of the whole parameter
calculation cycle.
--
Michael

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