Horton

Re: make MaxBackends available in _PG_init

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: "Bossart, Nathan" <bossartn@amazon.com>
Cc: Robert Haas <robertmhaas@gmail.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: 2022-01-27T00:56:04Z
Lists: pgsql-hackers 
On Tue, Jan 25, 2022 at 07:30:33PM +0000, Bossart, Nathan wrote:
> I think the patch is in decent shape.  There may be a few remaining
> places where GetMaxBackends() is called repeatedly in the same
> function, but IIRC v4 already clears up the obvious ones.  I don't
> know if this is worth worrying about too much, but I can create a new
> version if you think it is important.

There are such cases in FindLockCycleRecurse(), GetLockConflicts(),
GetLockStatusData() and InitProcGlobal(), as far as I can see.

Hmm.  I have been looking at this patch, and the lack of centralized
solution that could be used for other GUCs worries me like Fujii-san,
even if this would prevent an incorrect use of MaxBackends in contexts
where it should not be used because it is not initialized yet.  I
don't think it is a good idea in the long-term to apply this as-is.
--
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