GenerationType.SEQUENCE generates ID's which are already existing - spring

Question

I have a spring boot application which is already running online for several months without any problems until today. I have a Entity with id generation type sequence:
#Entity
#ComponentScan
public class MyEntity {
/**
*
*/
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE)
private long id;
}
Since today im getting errors when a new entity is created and stored:
Unique index or primary key violation: "PRIMARY_KEY_D92 ON PUBLIC.MyEntity(ID) VALUES (3713, 250)"; SQL statement:
Everytime when this error occurs the generated id (3713 in this case) is already existing in the database. So why all of a sudden the GenerationType.SEQUENCE is generating ids which are already existing?
EDIT
I use the H2 Database version 1.4.191

Answer 1

I've encountered this problem with Hibernate, but we had explicit #SequenceGenerator annotations. The problem is that the default SequenceGenerator in JPA has an allocationSize of 50, where as the default database sequence increments by 1. Those two values need to be the same. One solution is to define your SequenceGenerator and explicitly set that allocationSize.
#SequenceGenerator(name = "my_entity_gen", sequenceName = "my_entity_id_seq", allocationSize = 1)
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "my_entity_gen")
Generators must be unique, unless you want two tables to share them.
The other solution is to use a different generation strategy.
#GeneratedValue(strategy = GenerationType.IDENTITY)
This works if the database already knows to query the sequence upon inserting, as they usually do, unless you've explicitly created the sequence after the table.
The first approach will trigger two queries to the database for every insert, so it's almost certainly less efficient.