Re: make MaxBackends available in _PG_init

On Thu, Apr 14, 2022 at 12:22 PM Nathan Bossart
<nathandbossart@gmail.com> wrote:
> > I'd be in favor of a hard break.  There are already multiple extensions that
> > relies on non final value of GUCs to size their shmem request.  And as an
> > extension author it can be hard to realize that, as those extensions work just
> > fine until someone wants to try it with some other extension that changes some
> > GUC.  Forcing shmem request in a new hook will make sure that it's *always*
> > correct, and that only requires very minimal work on the extension side.
>
> Yeah, this is a good point.  If we're okay with breaking existing
> extensions like this, I will work on a patch.

I tend to think it's a good idea. It's not great to inconvenience
extension authors, but I think that with the kind of design we are
talking about here it will be pretty straightforward to see how to
update your extension: move the code that request shmem resources into
the new hook. If you want to be compatible with older PostgreSQL
releases by conditional compilation, conditionally call that function
from _PG_init() when PG_VERSION_NUM < whatever.

Compare that with the current situation, where things seem to mostly
work but sometimes don't, and it's not quite clear what to do about
it.

-- 
Robert Haas
EDB: http://www.enterprisedb.com