Why such poor performance?

[paul.degt]

I was thinking to switch to OpenJPA from Spring JDBC, just recently run 
a very simple test with 2 classes, SQL insert basically, the difference 
between plain JDBC and OpenJPA is more than 7 times!
Why such poor performance? Below is my sample code and results, I used 
Enhancer as JVM argument, actually without it JPA result was almost 
twice faster!

public static void main(String[] args) {
      
      
       Bill bill = new Bill();
       int id = new JVMRandom().nextInt(Integer.MAX_VALUE);
       bill.setId(id);
       bill.setCreated(new Date());
       bill.setPurchaseid(501253634);
       bill.setStatus(1);
       // System.out.println("bill id=" + id);

       Product prod = new Product();
       prod.setId(1);

       BillProduct bp = new BillProduct();
       bp.setBillid(bill);
       bp.setId(new JVMRandom().nextInt(Integer.MAX_VALUE));
       bp.setProductid(prod);       
      
       StopWatch sw = new StopWatch();       
      

       try {
           Class.forName("org.postgresql.Driver");

           String url = 
"jdbc:postgresql://localhost/mydb?user=admin&password=admin";
           Connection conn = DriverManager.getConnection(url);
           conn.setAutoCommit(false);
          
           // System.out.println("bill id=" + id);
           sw.start();

           PreparedStatement pstm = conn
                   .prepareStatement("insert into bill(id, status, 
purchaseid, created) values (?, ?, ?, ?)");
           pstm.setInt(1, bill.getId());
           pstm.setInt(2, bill.getStatus());
           pstm.setInt(3, 501253634);
           pstm.setDate(4, new java.sql.Date(System.currentTimeMillis()));
           pstm.executeUpdate();
           pstm.close();

           pstm = conn
                   .prepareStatement("insert into bill_product(id, 
productid, billid) values (?, ?, ?)");
           pstm.setInt(1, new JVMRandom().nextInt(Integer.MAX_VALUE));
           pstm.setInt(2, 1);
           pstm.setInt(3, bill.getId());
           pstm.executeUpdate();
           pstm.close();

           conn.commit();
           sw.stop();

           System.out.println("jdbc time=" + sw.getTime());
           conn.close();

       } catch (Exception e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
      
       sw.reset();

      
       //openjpa
       id = new JVMRandom().nextInt(Integer.MAX_VALUE);
       bill.setId(id);
       bp.setId(new JVMRandom().nextInt(Integer.MAX_VALUE));

       // persist
       EntityManagerFactory emf = Persistence
               .createEntityManagerFactory("testjpa");
       EntityManager em = emf.createEntityManager();

       sw.start();

       em.getTransaction().begin();

       em.persist(bill);
       em.flush();
       em.persist(bp);

       em.getTransaction().commit();

       sw.stop();
       System.out.println("openjpa time=" + sw.getTime());    

    
       em.close();

   }



*Console output: *

jdbc time=78
93  testjpa  INFO   [main] openjpa.Runtime - Starting OpenJPA 1.2.0
203  testjpa  INFO   [main] openjpa.jdbc.JDBC - Using dictionary class 
"org.apache.openjpa.jdbc.sql.PostgresDictionary".
openjpa time=547