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

[Ovidio Mallo (JIRA)]

Add support for custom dirty checking during flush
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                 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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