Frank,
> I understand tuning PG is almost an art form, yet it should be based on
> actual usage patterns, not just by system dimensions, don't you agree?
Well, it's both. It's more that available RAM determines your *upper* limit;
that is, on Linux, you don't really want to have more than 20% allocated to
the shared_buffers or you'll be taking memory away from the kernel.
Within that limit, data size, query complexity and volume, and whether or not
you have long-running procedures tell you whether you're at the low end or
the high end.
To futher complicate things, these calculations are all going to change with
7.5.
--
-Josh Berkus
Aglio Database Solutions
San Francisco