Horton

Re: make MaxBackends available in _PG_init

Julien Rouhaud <rjuju123@gmail.com>

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From: Julien Rouhaud <rjuju123@gmail.com>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Robert Haas <robertmhaas@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: 2022-04-12T05:08:35Z
Lists: pgsql-hackers 
Hi,

On Mon, Apr 11, 2022 at 02:14:35PM -0700, Nathan Bossart wrote:
> On Mon, Apr 11, 2022 at 01:44:42PM -0700, Nathan Bossart wrote:
> > On Mon, Apr 11, 2022 at 04:36:36PM -0400, Robert Haas wrote:
> >> If we throw an error while defining_custom_guc is true, how will it
> >> ever again become false?
> > 
> > Ah, I knew I was forgetting something this morning.
> > 
> > It won't, but the only place it is presently needed is when loading
> > shared_preload_libraries, so I believe startup will fail anyway.  However,
> > I can see defining_custom_guc being used elsewhere, so that is probably not
> > good enough.  Another approach could be to add a static
> > set_config_option_internal() function with a boolean argument to indicate
> > whether it is being used while defining a custom GUC.  I'll adjust 0003
> > with that approach unless a better idea prevails.
> 
> Here's a new patch set.  I've only changed 0003 as described above.  My
> apologies for the unnecessary round trip.

It looks sensible to me, although I think I would apply 0003 before 0002.

+   if (process_shared_preload_libraries_in_progress &&
+       !allow_when_loading_preload_libs)
+       ereport(ERROR,
+               (errcode(ERRCODE_CANT_CHANGE_RUNTIME_PARAM),
+                errmsg("cannot change parameters while loading "
+                       "\"shared_preload_libraries\"")));
+

I think the error message should mention at least which GUC is being modified.

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