Reasoning behind process instead of thread based architecture?

[Tim Sidemark]

Hello!

It would be interesting to know why MySQL has chosen a thread based architecture as opposed to a process based one. PostgreSQL uses a process based arch. They say that:

"The developers agree that multiple processes provide
more benefits (mostly in stability and robustness) than costs (more
connection startup costs). The startup costs are easily overcome by
using connection pooling.
"

So why has MySQL chosen a threaded approach? Also, each connection is a thread and each thread can run on multiple CPU:s. But can each query inside a thread itself become a thread thus run on multiple CPU:s?

I appreciate any answers.

Thank you.

Tim