Re: make MaxBackends available in _PG_init

From: Nathan Bossart <nathandbossart(at)gmail(dot)com>
To: Julien Rouhaud <rjuju123(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Michael Paquier <michael(at)paquier(dot)xyz>, "Bossart, Nathan" <bossartn(at)amazon(dot)com>, Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>, "wangsh(dot)fnst(at)fujitsu(dot)com" <wangsh(dot)fnst(at)fujitsu(dot)com>, Bharath Rupireddy <bharath(dot)rupireddyforpostgres(at)gmail(dot)com>, Greg Sabino Mullane <htamfids(at)gmail(dot)com>, "pgsql-hackers(at)lists(dot)postgresql(dot)org" <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: make MaxBackends available in _PG_init
Date: 2022-04-19 15:46:58
Message-ID: 20220419154658.GA2487941@nathanxps13
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On Tue, Apr 19, 2022 at 05:49:13PM +0800, Julien Rouhaud wrote:
> On Mon, Apr 18, 2022 at 08:17:04PM -0400, Tom Lane wrote:
>> Nathan Bossart <nathandbossart(at)gmail(dot)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.)
> Agreed. Similarly the process_shared_preload_libraries_in_progress flag could
> be modified by extension, and that wouldn't be any better.
>> 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.
> While at it, should we make process_shmem_requests_in_progress true when the
> new hook is called? The hook should only be called when that's the case, and
> extension authors may feel like asserting it.

Okay, I did it this way in v5.

Nathan Bossart
Amazon Web Services:

Attachment Content-Type Size
v5-0001-Fix-comments-about-bgworker-registration-before-M.patch text/x-diff 3.0 KB
v5-0002-Add-a-new-shmem_request_hook-hook.patch text/x-diff 12.7 KB

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