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

[Shawn Clowater (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3910?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=44742#comment-44742 ] 

Shawn Clowater commented on HHH-3910:
-------------------------------------

Steve, glad to hear about the better performance.  I'll have to search to see if the gains were documented anywhere, that might make my request to get some time to roll up to 4 higher priority.

On the skipDirtyCheck bit, I agree, I'm not a huge fan of having to implement an interface which is why I went down the persister path (we're already tapping into a custom persister for auditing and some filter massaging and it's a bit of a decent fit.)

I think the place where I did run into trouble is in the case where a many to one was deleted and Hibernate circled back and tried to update the property to null.  IIRC, that was the case that was slipping through the cracks for me, it didn't update my entity directly (which didn't update my map) but the loaded/current arrays were different lengths.

> custom dirty flag tracking
> --------------------------
>
>                 Key: HHH-3910
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3910
>             Project: Hibernate Core
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 3.3.1
>            Reporter: Ovidio Mallo
>              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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