Since 6bc8ef0b, InitializeMaxBackends() has used max_worker_processes
instead of adapting MaxBackends to the number of background workers
registered by modules loaded in shared_preload_libraries (at this time,
bgworkers were only static, but gained dynamic capabilities as a matter
of supporting parallel queries meaning that a control cap was
necessary).
Some comments referred to the past registration logic, making them
confusing and incorrect, so fix these.
Some of the out-of-core modules that could be loaded in this path
sometimes like to manipulate dynamically some of the resource-related
GUCs for their own needs, this commit adds a note about that.
Author: Nathan Bossart
Discussion: https://postgr.es/m/20220127181815.GA551692@nathanxps13
5ecd0183fb