Not necessarily. It's almost impossible for a CBO to get the best query plan for every query under every load under all data distributions. But the relational model is still beautiful, I find its limitations are minor in the grand scheme of things.

"It's almost impossible for a CBO to get the best query plan for every query under every load under all data distributions."

It's also impossible for a human to do it. At least the optimizer will be awake at 3 in the morning and able to respond to data changes; the human will be asleep.

I'm not disagreeing :-)

Although the poor DBA on pager may not agree with you.