[libraryofbabel]

There is some overlap, but they complement each other. This one (Database Internals) has much more of a technical deep dive on storage engines, especially B-tree implementation details.

If I was mentoring someone learning this stuff, I'd advise reading Designing Data Intensive Applications first, which is certainly the best for giving the big picture, and follow up with this one for more detail on certain topics.

Given the previous dearth of books on this important subject, I think it's wonderful that we have two.