Look at the History
There are a lot of analogies that you can use in debugging computer systems. One is a trip to the doctor's office. When you first go to a doctor, the first thing that happens is that he takes your medical history. You need to do the same thing with your database system. It is very rare that a problem just comes out of the blue. Something usually has to happen; something needs to change in the system to cause a new problem to occur. It's your job to evaluate whether or not one of these changes has caused your system to begin generating errors.
Keep a System Log
If you want to evaluate the effects of past system changes on your database system, it helps to have one place where all changes to the system are tracked. Various parts ...