Jpa generatedValue skipping values

Question

I have the next problem

POJO
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long idUser;

@Email
@Column(length = 64, unique = true)
private String email;

When the email constrains fail, the next generated entity doesn't follow the previous id.

So, it goes like 1 2, (email constraint fails), 4. Jpa skipped number 3....

Answer 1

This is normal for many databases; to support concurrent transactions, underlying sequence numbers may be incremented by transactions that are later rolled back, but the database doesn't attempt to "fill in" the missing values, since it would be prohibitive to keep track of them.