Part 2, Chapter 15
Every new chapter of my book is released right after it’s being completed, so the reader doesn’t have to wait for the whole part to be finished to get access to new material.
Table of content
This chapter explains how fetching works in Hibernate.
15.1 DTO projection
15.1.1 DTO projection pagination
15.1.2 Native query DTO projection
15.2 Query fetch size
15.3 Fetching entities
15.3.1 Direct fetching
188.8.131.52 Fetching a Proxy reference
184.108.40.206 Natural identifier fetching
15.3.2 Query fetching
15.3.3 Fetching associations
220.127.116.11.1 The N+1 query problem
18.104.22.168.2 How to catch N+1 query problems during testing
22.214.171.124.4 The Open Session in View Anti-Pattern
126.96.36.199.5 Temporary Session Lazy Loading Anti-Pattern
188.8.131.52 Associations and pagination
15.4 Query plan cache
Fetching data has a great impact on data access layer performance, and fetching way too much data is one of the most common performance-related issues. In this chapter, I explain when you should use entity fetching and when to switch to DTO projections.
There is also a very interesting example which demonstrates why, sometimes, processing data in the database (Recursive CTE, Window Functions) can outperform application-level data processing.
FetchType.EAGER is often a good hint that an application might experience performance issues. But
FetchType.LAZY is not without problems either because it can lead to N+1 query problems or
Unfortunately, there are also some widespread anti-patterns such as
Open Session in View or Temporary Session Lazy Loading which cure the symptoms and do not address the root cause of a
A lesser-known configuration is the query plan cache, and you’ll also learn how you can tune it, and for which queries it makes more sense to save the pre-compilation phase.
Enjoy reading High-Performance Java Persistence!
P.S. There is also a Google Group dedicated to this book, so, if you’d like to join and discuss the book content, don’t hesitate to join in.