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Chapter 13. Batch Processing

13.1. About Batch Processing

A naive approach to inserting 100,000 rows in the database using Hibernate might look like this: 
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
for ( int i=0; i<100000; i++ ) {
    Customer customer = new Customer(.....);
    session.save(customer);
}
tx.commit();
session.close();
Depending on your environment setup, this approach will likely fail with an OutOfMemoryException. That is because Hibernate caches all the newly inserted Customer instances in the session-level cache. In this chapter we will show you how to avoid this problem.
If you are undertaking batch processing you will need to enable the use of JDBC batching. This is absolutely essential if you want to achieve optimal performance. Set the JDBC batch size to a reasonable number (10-50, for example): 
hibernate.jdbc.batch_size 20
Hibernate disables insert batching at the JDBC level transparently if you use an identity identifier generator.
You can also do this kind of work in a process where interaction with the second-level cache is completely disabled: 
hibernate.cache.use_second_level_cache false
However, this is not absolutely necessary, since we can explicitly set the CacheMode to disable interaction with the second-level cache.
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