query for nextval sequence generation taking long time - postgresql

Question

I have a process in application where we insert 1000+ records in application. There is a attribute in the table as mentioned below.
#Index(name = "_IDX_UNIQUE_UUID", columnNames = {"UUID"})
#Column(name = "UUID", nullable = false)
private Long uuid;
During populating the entity class the value is set as following
entity.setUuid(service.getNextUuid());
which calls this method in service class:
public Long getNextUuid() {
Query query = entityManager.createNativeQuery("select nextval('seq_xxxx_uuid')");
//This takes lot of time to execute
Obj result = query.getSingleResult();
return ((BigInteger) result).longValue();
}
To get next value from sequence, it takes around 200-700 ms. This accumulates to several minutes if I try to insert 1000+ records. Moreover, the query is quite simple and executes in less than 1ms if I execute it in a database client.
I am using postgresql 9.4-1206-jdbc4, hibernate 4.2.0.Final and Spring 4.2.5.

Answer 1

It's slow, because you're going through all the layers of security and consistency checks of a JPA full query, plus you're creating a new NativeQuery object every time and not doing it though a #NamedNativeQuery, thus taking even more time to evaluate.
The solution is to annotate the column with:
#Id
#Index(name = "_IDX_UNIQUE_UUID", columnNames = {"UUID"})
#SequenceGenerator(name = "seq_xxxx_uuid_gen", sequenceName = "seq_xxxx_uuid", allocationSize = 1)
#GeneratedValue(generator = "seq_xxxx_uuid_gen")
#Column(name = "UUID", nullable = false)
private Long id;
You do want that allocationSize to be the same value as the increment_by value of your sequence, or you'll have other problems after the first persist.
If you need to use that Id for multiple objects (say it's part of a composite key, but only part of it is serial-generated), just grab it from the first one after persisting it.
Edit:
Alternatively you can forego the SequenceGenerator and use this:
#GeneratedValue(strategy = GenerationType.IDENTITY)
It may be faster, if the generated query is properly optimized and uses java.sql.Statement.getGeneratedKeys() upon insert.