How To Quickly Reproduce The N+1 Performance Issue

Description: The N+1 is an issue of lazy fetching (but, eager is not exempt). This application reproduce the N+1 behavior.

Key points:

• define two entities, Author and Book in a lazy bidirectional @OneToMany association
• fetch all Book lazy, so without Author (results in 1 query)
• loop the fetched Book collection and for each entry fetch the corresponding Author (results N queries)
• or, fetch all Author lazy, so without Book (results in 1 query)
• loop the fetched Author collection and for each entry fetch the corresponding Book (results N queries)

Output example: