> The main big table "data" has about 1.2 billion rows and the "data_set"
> table has about 800 million rows. I was wrong about the result set size
> in my stackoverflow post, the result set varies but is usually around 10
> million rows (it can be more but not on average).

Out of curiosity: what to hell are you doing with this result set?
You definitely can't either print it on paper or show to user.
The only thing that you can do in this situation - put temp space
which FB uses for sorting onto separate HDD or even better onto SSD.

SY, SD.