If "Readings in Database Systems" is your cup of tea you should probably consider

* Database Internals (https://www.oreilly.com/library/view/database-internals/9781...) - very recent and of manageable size

* Database System Concepts (https://www.amazon.com/Database-Concepts-Abraham-Silberschat...) - specifically, the chapters on storage and query processing, it's a huge volume otherwise. Also, "Database Systems: The Complete Book" is basically an older version of it.