Will committing multiple transactions during one session increase performance?

Question

I want to be able to use one entity manager to commit multiple transactions for CRUD actions concerning different entity objects. For example I want to be able to delete a cat entity object and create a new dog entity object all during one entity manager session. I achieve this by having the catService and dogService (the objects that can CRUD objects) extend a GenericService:

public abstract class GenericService<T> {
private Class<T> type;
protected static EntityManager entityManager;

public GenericService() {
    Type t = getClass().getGenericSuperclass();
    ParameterizedType pt = (ParameterizedType) t;
    type = (Class) pt.getActualTypeArguments()[0];
    if (entityManager == null || !entityManager.isOpen()) entityManager = GetEntityManager.getInstance(); // zo kunnen meerdere services gebruik maken van dezelfde entitymanager sessie. 1 operation per sessie is een antipattern namelijk. Beter meerdere operations in 1 sessie doen.
}

// sluit entityManager en daarmee dus ook de sessie af.
public void close(){
    entityManager.close();
}

Now both services share the same entitymanager. Now I can make multiple transactions and call the inherited close() method only on the last Service object, which then closes the shared entity manager.

I intend to make a webapplication so I was wondering if using entity manager sessions more efficiently by having them be shared by different serviceObjects that are operating upon different entity objects would have a performance gain compared to opening and closing a new session(entity manager) for just one transaction.

Thank you.

Answer 1

Session-per-operation is an anti-pattern but not for performance reasons. You can do a lot of extra calculations (like creating sessions) and not notice any performance difference because waiting for a database to complete a transaction takes a long time compared to doing extra calculations (database I/O operations take milliseconds to complete, calculations take nanoseconds to complete).

Since you intend to make a web-application, try using Hibernate's sessionFactory.getCurrentSession() which sort of does what you do now in the constructor of the GenericService - more info in the user guide, this answer and javadocs.