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. Fetching 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 22.214.171.124 Fetching a Proxy reference 126.96.36.199 Natural identifier fetching 15.3.2 Query fetching 15.3.3 Fetching associations 188.8.131.52 FetchType.EAGER 184.108.40.206 FetchType.LAZY 220.127.116.11.1 The N+1 query problem 18.104.22.168.2 How to catch N+1 query problems during testing 22.214.171.124.3 LazyInitializationException 126.96.36.199.4 The Open Session in View Anti-Pattern 188.8.131.52.5 Temporary Session Lazy Loading Anti-Pattern 184.108.40.206 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 precompilation 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.