> Did you have any specific ideas in mind?

Some ideas comes to my mind, but being not an expert in thread-
programming I can say ingenuous things.
Never mind, here they come:
- move subqueries (those heavy ones) onto another thread
- divide the job onto threads on a per-table basis
- let threads create useful temporary indexes on the fly
- let the optimizer run on a separate thread
- use threads to keep index selectivity updated

Mirco