Hibernate: Optimize updates with @DynamicUpdate

When using Hibernate as a layer between your Java code and the Database layer you release control on how the actual SQL query is generated. Hibernate will generate from the HSQL you write the “best” query. That “best” is in fact sometimes sub-optimal.
A very important Hibernate 4 (make sure you have at least 4.2.5) annotation that controls how an update behaves is @DynamicUpdate.
By default the Hibernate behaviour is to update all the fields of a an entity, so in fact @DynamicUpdate(false)

Take for example the following entity:

@Entity
@DynamicUpdate(true)
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
@Table(name = "OutputBulkBuffer")
public class OutputBulkBuffer {
	
	/**
	 * Content of the byte message
	 */
	@Lob
	protected byte[] byteContent;
	
	@Column(length = 50)
	protected String status;
	
	public byte[] getByteContent() {
		return byteContent;
	}
	
	public void setByteContent(byte[] byteContent) {
		this.byteContent = byteContent;
	}
	
	public void setStatus(Status status) {
		if (status != null) {
			this.status = status.getName();
		} else {
			this.status = null;
		}
	}
	
	public void setStatus(String status) {
		this.status = status;
	}
}

When I update the status of a list of objects of this type from READY to DELIVERED the update generated by Hibernate will update also the column holding the LOB. You can imagine the problem here if your LOB is on average 10MB and your update is done on 1000 objects.

update OutputBulkBuffer set byteContent=?, status=? where id=?

After I add the annotation @DynamicUpdate(true) and I do the same update of the status the update generated by Hibernate will be:

update OutputBulkBuffer set status=? where id=?

This can have a huge difference in performance.