You will find hereafter a number of scripts which we find useful when studying performance problems.
Most of them access tables (or views) an ordinary user cannot query, so you may have to negotiate in order to run them.
Actually, you may even need the right to query the tables in the SYS schema, and not only the catalog. When you work on performance you become impatient and some of the queries would be desperately slow if run against the dictionary view. After all, when you go to the surgeon you don’t expect to keep buttoned up ... if you want any result, that is.
All those scripts are published as is, without any guarantee, and under the GPL license.