Beginning tuning

I'm just getting started on the process of analyzing performance for a Java Enterprise application.  (The main negative symptom at the moment is that it doesn't use more than three processors on an eight-processor system, regardless of load.)

One of the first things I've noticed out of a number of thread dumps is that there's about an 80% chance that the stack points to I/O requests from PGStream.ReceiveChar().  I'm wondering about any hints or pointers that would help me understand whether that's expected behavior, or something that needs fixing, or just generally how to evaluate/improve JDBC performance.

(Regarding the main problem, none of my threads are reported in a blocked state, leading to my focus on I/O.)