[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-3910) Add support for custom dirty checking during flush

[Ovidio Mallo (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3910?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=33150#action_33150 ] 

Ovidio Mallo commented on HHH-3910:
-----------------------------------

Shawn, thanks for the feedback!

Indeed, it is in EntityEntry#requiresDirtyCheck(Object entity) where the current dirty check using bytecode instrumentation is performed. So adding support for a custom dirty checking at the place where this method is called (in DefaultFlushEntityEventListener) as you are suggesting would already give the desired performance gain. If following this approach, I think it would also be important for clients to have a clear hook where they can clear their custom dirty flag (after flush), ideally also inside the DefaultFlushEntityEventListener class to keep it close to the actual dirty checking code.

BTW, I've also posted another JIRA issue regarding the performance of the FieldInterceptionHandler class which is important when using bytecode instrumentation. I've attached a patch to that issue which significantly improves the performance of the functionality provided by that class which in turn has a positive impact on the flush performance, especially if bytecode instrumentation is used for dirty checking during flush. Using my patch, flushing a large number of non-dirty objects becomes about 6-7 times faster when using bytecode instrumentation (see the measurements presented there) for dirty checking, so I would expect at least the same performance gain with the approach you are suggesting with the additional advantage that you don't need any bytecode instrumentation. For the patch and some performance measurements, please see the following JIRA issue:
  http://opensource.atlassian.com/projects/hibernate/browse/HHH-3909

> Add support for custom dirty checking during flush
> --------------------------------------------------
>
>                 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
>
> 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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