"Andy B" <abhousehuntRE-M--O--V-E@blueyonder.co.uk> writes:
> 1. set postgresql.conf->shared_buffers to a value like (40GB/8KB),
That is the very last thing you want to do (even if you could, which you
can't). Let the OS manage the memory --- the kernel can do just fine at
caching large files in RAM. I've never seen any evidence that it helps
to set shared_buffers higher than a few tens of thousands.
See the pgsql-performance archives for much more on this subject.
regards, tom lane