In order to get a deeper understanding of PostgreSQL, I started working diligently through this book. It’s written by Hans-Jürgen Schönig, the CEO of Cybertec. We consulted with Cybertec in 2012 when we had database issues with Wunderlist and they offered first-class support.
The book gives a good overview of topics such as Transactions and Locking, Making Use of Indexes (understanding simple queries and the cost model, the different index types such as B-Tree GiST and Gin indexes etc.), Log Files, Optimizing Queries, Backups and Replication and many more. I looked at various other PostgreSQL books and this one stood out as it’s well-written and touches on the right topics.
The book is 29.99 Euro for the print edition, including the DRM free ebooks as PDF, EPUB and Mobi. Or only 18.89 Euro just for the ebooks.