Database Replay is a feature in EM12c that a lot of folks are unfamiliar with, but once they learn about it, well, now then they figure out how valuable it really is.  Where the ADDM Comparison Report comes in really handy when you want to see what changed, think about how much more value there is if you could test out what a change in parameters, patches, or in code would do to a database and THEN use the ADDM Comparision Report to view the “What if’s”?  This is where Database Replay really enhances the comparison report feature. along with…