I haven't fully read it (yet), but based on a quick scan of a few chapters, it looks like a dense but well-written introduction.

Some additional resources I'd recommend if you're interested:

Designing Data-Intensive Applications is a fantastic place to start if you're interested in the intersection of databases & distributed systems:

https://dataintensive.net/

The Architecture of Open-Source Applications book has a fewer chapters on databases:

https://aosabook.org/en/bdb.html

https://aosabook.org/en/hdfs.html

https://aosabook.org/en/nosql.html

There's some fantastic documentation on Postgres and its internals:

http://www.interdb.jp/pg/index.html

https://momjian.us/main/presentations/internals.html

https://www.postgresql.org/docs/current/internals.html