Re: make MaxBackends available in _PG_init

On Mon, Aug 2, 2021 at 2:18 PM Bossart, Nathan <bossartn(at)amazon(dot)com> wrote:
> I just encountered the same thing, so I am bumping this thread. I was
> trying to use MaxBackends in a call to RequestAddinShmemSpace() in a
> _PG_init() function for a module, but since MaxBackends is not yet
> initialized, you essentially need to open-code InitializeMaxBackends()
> instead.
>
> I think the comments about needing to register background workers
> before initializing MaxBackends have been incorrect since the addition
> of max_worker_processes in v9.4 (6bc8ef0b). Furthermore, I think the
> suggested reordering is a good idea because it is not obvious that
> MaxBackends will be uninitialized in _PG_init(), and use-cases like
> the RequestAddinShmemSpace() one are not guaranteed to fail when
> MaxBackends is used incorrectly (presumably due to the 100 KB buffer
> added in CreateSharedMemoryAndSemaphores()).
>
> I've attached a new version of the proposed patch with some slight
> adjustments and an attempt at a commit message.

I think this is a good idea. Anyone object?

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