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: Nathan Bossart <nathandbossart@gmail.com>
Cc: Robert Haas <robertmhaas@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: 2022-04-12T21:46:36Z
Lists: pgsql-hackers 
Nathan Bossart <nathandbossart@gmail.com> writes:
> If we allow changing GUCs in _PG_init() and provide another hook where
> MaxBackends will be initialized, do we need to introduce another GUC flag,
> or can we get away with just blocking all GUC changes when the new hook is
> called?  I'm slightly hesitant to add a GUC flag that will need to manually
> maintained.  Wouldn't it be easily forgotten?

On the whole I think Robert's got the right idea: we do not really
need an enforcement mechanism at all.  People who are writing
extensions that do this sort of thing will learn how to do it right.
(It's not like there's not a thousand other things they have to get
right.)

			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