Nathan Bossart <nathandbossart@gmail.com> writes:
> I think it'd be reasonable to allow changing custom GUCs in _PG_init().
> Those aren't going to impact things like MaxBackends.
It's reasonable to allow changing *most* GUCs in _PG_init(); let us
please not break cases that work fine today.
It seems after a bit of reflection that what we ought to do is identify
the subset of PGC_POSTMASTER GUCs that feed into shared memory sizing,
mark those with a new GUC flag, and not allow them to be changed after
shared memory is set up. (An alternative to a new flag bit is to
subdivide the PGC_POSTMASTER context into two values, but that seems
like it'd be far more invasive. A flag bit needn't be user-visible.)
Then, what we'd need to do is arrange for shared-preload modules to
receive their _PG_init call before shared memory creation (when they
can still twiddle such GUCs) and then another callback later.
regards, tom lane