[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-3910) custom dirty flag tracking

[Steve Ebersole (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3910?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=45225#comment-45225 ] 

Steve Ebersole commented on HHH-3910:
-------------------------------------

Not sure exactly where to fit this in the existing documentation.  It does not see to fit nicely anywere.  Maybe y'all have some suggestions?

In the meatime, I'll quickly document its use here and write a blog entry tomorrow.

The contract here is named {{org.hibernate.CustomEntityDirtinessStrategy}}.  It defines only 3 methods:
{code:title=CustomEntityDirtinessStrategy.java|borderStyle=solid}
public interface CustomEntityDirtinessStrategy {
	/**
	 * Is this strategy capable of telling whether the given entity is dirty?  A return of {@code true} means that
	 * {@link #isDirty} will be called next as the definitive means to determine whether the entity is dirty.
	 *
	 * @param entity The entity to be check.
	 * @param session The session from which this check originates.
	 *
	 * @return {@code true} indicates the dirty check can be done; {@code false} indicates it cannot.
	 */
	public boolean canDirtyCheck(Object entity, Session session);

	/**
	 * The callback used by Hibernate to determine if the given entity is dirty.  Only called if the previous
	 * {@link #canDirtyCheck} returned {@code true}
	 *
	 * @param entity The entity to check.
	 * @param session The session from which this check originates.
	 *
	 * @return {@code true} indicates the entity is dirty; {@link false} indicates the entity is not dirty.
	 */
	public boolean isDirty(Object entity, Session session);

	/**
	 * Callback used by Hibernate to signal that the entity dirty flag should be cleared.  Generally this
	 * happens after previous dirty changes were written to the database.
	 *
	 * @param entity The entity to reset
	 * @param session The session from which this call originates.
	 */
	public void resetDirty(Object entity, Session session);
{code}

This is what your code would implement.  You specify this using the {{hibernate.entity_dirtiness_strategy}} setting (org.hibernate.cfg.AvailableSettings#CUSTOM_ENTITY_DIRTINESS_STRATEGY}}).  

That's basically it.

> custom dirty flag tracking
> --------------------------
>
>                 Key: HHH-3910
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3910
>             Project: Hibernate ORM
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 3.3.1
>            Reporter: Ovidio Mallo
>            Assignee: Steve Ebersole
>              Labels: performance
>             Fix For: 4.1.0
>
>         Attachments: DirtyCheckFailedAttempt.patch
>
>
> Currently, Hibernate supports a special dirty checking on instrumented entities
> in order to improve the flush performance. IMO, this optimization can often be
> rather significant. However, the drawback is that you have to use bytecode
> instrumentation in order to take advantage of this performance improvement which
> might not be an option in some projects.
> Therefore, I wanted to propose to extend the current dirty checking during flush
> in such a way that the dirtyness information can also be directly provided by
> clients. Thereby, I could think of two possible approaches to do this:
> 1. Introduce an interface which client entities might implement in case they
>    have some notion of dirtyness. The interface could look something like:
>      public interface DirtyAwareEntity {
>        boolean getMightBeDirty();
>        void setMightBeDirty(boolean mightBeDirty);
>      }
>    Using such an interface, Hibernate could easily check whether an entity might
>    be dirty during flush and it could also reset the dirty flag after flush just
>    as is currently done for instrumented classes. So this approach would probably
>    be rather easy to implement and very convenient for clients since they would
>    only have to implement that interface on the appropriate entities and set the
>    dirty flag when the entity is actually modified.
> 2. Add some hooks on event listeners and/or on the Interceptor for querying whether
>    an entity is dirty and for resetting the dirty flag. E.g. one could add the
>    following hook method to the DefaultFlushEntityEventListener class:
>      protected boolean requiresDirtyCheck(FlushEntityEvent event);
>    By default, this method would call EntityEntry#requiresDirtyCheck(Object entity)
>    as is done right now.
>    Resetting the dirty flag could maybe be done in Interceptor#postFlush() or some
>    dedicated method could be provided.
> BTW, I know that currently there already is the Interceptor#findDirty() method which
> already allows for some custom dirty checking but the problem from a performance
> point of view is that this method requires the entity's property values as parameter
> which are retrieved in DefaultFlushEntityEventListener#getValues() which is the most
> expensive method during flush. This drawback of the findDirty() method has often been
> noticed in comments on the news groups.
> I personally think it would be nice if something could be done to improve the
> performance of flushing in Hibernate since from what I read on the news groups and
> the like, flushing still seems to often lead to performance problems in practice,
> especially in larger projects where it is often not easy to avoid flushes or to
> keep the numer of entities in the session cache small. In fact, we are having quite
> some trouble with that in our project and having some custom dirty checking like the
> one I'm proposing here would greatly help in our project and in other projects as
> well, I guess.

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