Question

I use OpenJPA 2.2.0 on WebSphere Application Server 8 with a MySQL 5.0 DB.

I have a list of objects which I want to merge into the DB.

it’s like:

for (Object ob : list) {
            Long start = Calendar.getInstance().getTimeInMillis();
            em = factory.createEntityManager();
            em.getTransaction().begin();

            em.merge(ob);

            em.getTransaction().commit();
            em.close();
            Long end = Calendar.getInstance().getTimeInMillis();
            Long diff = end - start;
            LOGGER.info("Time: " + diff);
        }

When I run this loop I need about 300-600 Milliseconds to merge one object. When I delete the line “em.merge(ob);” then I need “0” Milliseconds to iterate over 1 List Object.

So my question is: What can I do to improve the time to merge one object?

Thanks!

Answer 1

You can try starting the transaction before iteration & then commiting it afterwards within a single transaction. So, basically you are creating a batch which would be merged/persisted on commit.

Also, you can limit the number of objects in a batch to be processed at a time & can explicitly flush the changes into database.

Here, you are initiating a transaction & commiting it in each iteration and also creating/closing entity manager each time, will affect performance for numerous data.

It will be something like below code.

em = factory.createEntityManager();
em.getTransaction().begin();
int i = 0;

   for (Object ob : list) {
       Long start = Calendar.getInstance().getTimeInMillis();

       em.merge(ob);

       Long end = Calendar.getInstance().getTimeInMillis();
       Long diff = end - start;
       LOGGER.info("Time: " + diff);

       /*BATCH_SIZE is the number of entities 
            that will be persisted/merged at once */

       if(i%BATCH_SIZE == 0){    
           em.flush();
           em.clear(); 
       }

       i++;
   }

em.getTransaction().commit();
em.close();

Here, you can also rollback the whole transaction if any of the object fails to persist/merge.