I would assume that any book about the internals of a database would be suitable. MySQL is plenty real enough to be educational to learn about its internals, yea verily, even its quirks, and to learn a lot about how other databases work. Even the "NoSQL" databases will use many of the same primitives.
An equivalent substitution for another database would be fine; anyone have any suggestions? Then again, such a substitution is really solving a non-problem.
It may very well be the case that looking at the internals of some database other would provide a different set of lessons.
IMHO, MySQL is especially ugly due to an attempt to insert an abstract interface around its storage engines. IIRC that interface is leaky, and its documentation is pretty spotty. Also, the InnoDB storage engine has a lot of complexity that seemingly duplicates what's provided on the storage-engine-agnostic side of that interface.
One of the big lessons I took away from studying MySQL's internals, and partially confirmed by the "internals" book, was this: Be careful when designing a plugible storage-engines framework for a DBMS; MySQL has some examples of what can go wrong.
That's something you're unlikely to find mentioned in a generic DBMS-implementation book, but is very good to know about regardless.
An equivalent substitution for another database would be fine; anyone have any suggestions? Then again, such a substitution is really solving a non-problem.