Horton

Re: make MaxBackends available in _PG_init

Michael Paquier <michael@paquier.xyz>

View thread View on postgr.es
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: 2022-01-25T08:00:56Z
Lists: pgsql-hackers 
On Mon, Jan 10, 2022 at 07:01:32PM +0000, Bossart, Nathan wrote:
> On 1/7/22, 12:27 PM, "Robert Haas" <robertmhaas@gmail.com> wrote:
>> On Fri, Jan 7, 2022 at 1:09 PM Bossart, Nathan <bossartn@amazon.com> wrote:
>>> While that approach would provide a way to safely retrieve the value,
>>> I think it would do little to prevent the issue in practice.  If the
>>> size of the patch is a concern, we could also convert MaxBackends into
>>> a macro for calling GetMaxBackends().  This could also be a nice way
>>> to avoid breaking extensions that are using it correctly while
>>> triggering ERRORs for extensions that are using it incorrectly.  I've
>>> attached a new version of the patch that does it this way.
>>
>> That's too magical for my taste.
> 
> Fair point.  v4 [0] is the less magical version.

So, where are we on this patch?  It looks like there is an agreement
that MaxBackends is used widely enough that it justifies the use of a
separate function to set and get a better value computed.  There may
be other parameters that could use a brush up, but most known cases
would be addressed here.  v4 looks rather straight-forward, at quick
glance.

(I'd also prefer the less magical version.)
--
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