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A related topic is that of profiling. This is where you find out which portions of your code get executed the most. You can use this to choose which code you need to optimize. Profiling gets turned on and off with the DBMS_HPROF built in package.
Just like with trace, you need to run the "dbmshprof.sql" script to set up the tables for profiling. There is even an option to view the profiling output in HTML form. Next time I am going to talk about the hot topic of SQL injection attacks. Until then, be good.