[needusername]

> Really? I have a book on CBO performance troubleshooting from the foremost expert and even he says that he can't fully understand why the CBO does the things it does.

> I doubt your in house experts fully understand the Oracle CBO. They may claim they do, but unless they have access to material that isn't public they can't possibly be able to diagnose the CBO fully.

Maybe. Let me put it this way, so far they could explain all CBO decisions where we had performance issues.