Hi, On 2021-08-02 16:06:15 -0400, Robert Haas wrote: > On Mon, Aug 2, 2021 at 2:18 PM Bossart, Nathan <bossa...@amazon.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?
I'm not so sure it's a good idea. I've seen several shared_preload_library using extensions that adjust some GUCs (e.g. max_prepared_transactions) because they need some more resources internally - that's perhaps not a great idea, but there's also not an obviously better way. ISTM this would better be solved with making the hook or config logic for libraries a bit more elaborate (e.g. having a hook you can register for that's called once all libraries are loaded). Greetings, Andres Freund
