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>, 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>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2022-04-19T00:17:04Z
Lists: pgsql-hackers 
Nathan Bossart <nathandbossart@gmail.com> writes:
> I'm looking for a clean way to ERROR if someone attempts to call
> RequestAddinShmemSpace() or RequestNamedLWLockTranche() outside of the
> hook.  Currently, we are using static variables in ipci.c and lwlock.c to
> silently ignore invalid requests.  I could add a new 'extern bool' called
> 'process_shmem_requests_in_progress', but extensions could easily hack
> around that to allow requests in _PG_init().  Maybe I am overthinking all
> this and that is good enough.

If they do that and it breaks something, that's their fault not ours.
(It's not like there's not $BIGNUM ways for a C-language module to
break the backend, anyway.)

BTW, I'd make such errors FATAL, as it's unlikely that we can recover
cleanly from an error during initialization of a loadable module.
The module's likely to be only partially initialized/hooked in.

			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