java - Hibernate use of PostgreSQL sequence does not affect sequence table

Question

I've configured Hibernate to use PostgreSQL sequence (via annotations) to generate values for primary key id column as follows:

@Id 
@SequenceGenerator(name="pk_sequence",sequenceName="entity_id_seq")
@GeneratedValue(strategy=GenerationType.SEQUENCE,generator="pk_sequence")
@Column(name="id", unique=true, nullable=false)
public int getId() {
    return this.id;
}

What I see with this configuration is that hibernate is already assigning id values > 3000 on persisting, whereas the query on used sequence shows the following:

database=# select last_value from entity_id_seq;
last_value 
------------
     69

(1 row)

Questions:
Is there anything wrong or not?
Should hibernate sync with the sequence table?
If not, where does it store the last generated id?

Thank you.

Answer 1

I had the same problem. It is related to the id allocating strategies of Hibernate. Whe n you choose GenerationType.SEQUENCE, Hibernate uses HiLo strategy which allocates IDs in blocks of 50 by default. So you can explicitly set allocationSize value like this:

@Id 
@SequenceGenerator(name="pk_sequence",sequenceName="entity_id_seq", allocationSize=1)
@GeneratedValue(strategy=GenerationType.SEQUENCE,generator="pk_sequence")
@Column(name="id", unique=true, nullable=false)
public int getId() {
    return this.id;
}

Though, I've also heard opinions that using HiLo strategy with allocationSize=1 is not a good practice. Some people recommend to use GenerationType.AUTO instead when you have to deal with database-managed sequences

Update: I did end up going with allocationSize=1, and things seem to work as I expect now. My application is such that I don't really need blocks of IDs anyway, so YMMV.