Writing a book is difficult, but writing a book about performance and persistence is a real challenge.

If you want to understand how locking, sharding, replication, database concurrency control work, then this book is for you.
Vlad gives you plenty of tips and tricks on Hibernate, helping you diagnose your performance issues (e.g. mapping, fetching, or caching).

I learn a lot by reading his book and I highly recommend it if you use relational databases and ORM tools such as Hibernate.

This book is a highly recommended resource for every developer who is serious about learning and mastering the difficult topic of designing and implementing high performance Java database applications.

The book covers in detail the performance aspect of the plain JDBC and Hibernate programming, explains the theoretical and practical implications of the database transactions, and discusses some rare topics such as the database connection pool sizing and statement caching.

Good books on persistence are few and far between. This is something else - it's deeply researched but also entirely practical. I'm basically using it as a reference for everything SQL. Plus, the transaction chapter is a must read.