The application we'll be looking at (name changed to FRED to protect the innocent) is a well-known PHP content management system that has been in existence for over five years. No slights are intended against the developers of the code -- they created it with the intention of originally supporting MySQL alone.
But that makes it a perfect candidate for our purposes.
Note: I have an idea of how FRED's team is approaching some of these problems, and can share those with you along the way, but any approach requires trade-offs of some kind.