It depends on the VM you are using, if you have a JIT and your code benefits and scalability needs.
IBM has a good VM which is better than the stock one from Sun and Oracle's is great for scalability. Oracle's VM gets its performance from advance memory management, which is designed to scale and isolate volitale session memory from other sessions. This design allows Oracle's VM to scale with limited degradation.
It also depends on if your VM uses a JIT or not. A JIT is a just in time compiler, which increases performance by compiling natively portions of the code as needed. A JIT can work well depnding one the code. I do not know if Oracle's VM uses a JIT or not, but I remember reading something about a JIT in Oracle.
I have a friend that was employed by Oracle and he says that Oracle does not use Java in the DB, I do not know why.
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