Joe Lester <joe_lester@sweetwater.com> writes:
> That's odd. It's giving me a -1 for the shmmax value. I assume that's
> NOT normal. Why would that be?
It's not --- you should get back the same value you set. I speculate
that you tried to set a value that exceeded some internal sanity check
in the kernel. I wouldn't be too surprised if the kernel rejects values
larger than available RAM, for instance.
>> Note that there's not much percentage in setting shmmax higher than
>> shmall * pagesize.
> I'm not quite clear on this. Does this mean that shmmax and shmall
> should be set to the same value?
shmmax is the limit on a single shmget() request, in bytes. shmall is
the limit on total shared-memory allocation across all active shmget()
requests. So there's certainly no point in making the former larger
than the latter. Assuming that you only intend to have a single
Postgres postmaster requesting shared memory (I'm not sure whether there
are any components of OS X that request shared memory --- X11 might),
there's not much point in making the former smaller than the latter
either. Bear in mind though that shmall is measured in 4K pages not in
bytes. Thus the OS X factory-default settings of 4M and 1024 are in
fact both enforcing a 4MB limit.
regards, tom lane