Karl Arao has written a nice blog entry where he used also some of my tools for visualizing and understanding performance of a RAC cluster suddenly gone slow. He presents a systematic approach he used for gathering evidence and also hopefully you notice that having the ability to easily visualize performance data (with PerfSheet for example) can be very helpful and time saving when troubleshooting non-trivial problems.
Check his blog entry out here:
NB! After a 1.5 year break, this year’s only Advanced Oracle Troubleshooting training class (updated with Oracle 12c content) takes place on 16-20 November & 14-18 December 2015, so sign up now if you plan to attend this year!