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From Kevin Sutter <kwsut...@gmail.com>
Subject Re: pro & contra of using Multiple Persistence Units
Date Mon, 21 May 2012 13:10:54 GMT
OpenJPA's built-in cache does not synch the L2 caches.  You could configure
the remote event notification service [1], but that's kind of a cryptic way
of getting the cache synchronization to occur.  If you can pre-configure
your JMS endpoints or TCPIP ports, then this approach might work.  It's
been on the ToDo list to improve this built-in capability, but it just
hasn't risen in priority.

Other alternatives are to use one of the distributed cache plugins for
OpenJPA.  If you are a WebSphere customer, you could configure the
Dynacache plugin or the WebSphere Extreme Scale plugin.  Outside of
WebSphere, ehcache also provides a plugin for use with OpenJPA.  And, if
you are ambitious, writing an alternate plugin for your favorite
distributed cache is not out of the question.  I'd use the ehcache plugin
as an example.

Good luck,
Kevin

[1]
http://openjpa.apache.org/builds/latest/docs/docbook/manual.html#ref_guide_event

On Mon, May 21, 2012 at 1:37 AM, Boblitz John <John.Boblitz@bertschi.com>wrote:

> Hello Kevin,
>
> Thanks for your response.  Not so sure I can see a need in my circumstance,
> but at least it's not a "bad thing to do" :D - maybe I'll see some areas
> where
> this might come in handy ....
>
> As to the divergent states, I am mostly concerned about the Cache and
> ensuring that
> changes in one pu are "seen" in the other pu if that entity is cached.
>  Perhaps I'm being bull-headed
> here, but how can I synch the caches?
>
> Thanks again & Cheers,
>
> John
>
> > -----Ursprüngliche Nachricht-----
> > Von: Kevin Sutter [mailto:kwsutter@gmail.com]
> > Gesendet: Freitag, 18. Mai 2012 20:42
> > An: users@openjpa.apache.org
> > Betreff: Re: pro & contra of using Multiple Persistence Units
> >
> > John, in this case, thanks for the push...  :-)  I had missed
> > your first request...
> >
> > Using multiple persistence units is a fine practice and we
> > recommend that approach to many customers.  Even when dealing
> > with the same datasource, some applications (or facets of an
> > application) just require different configurations for
> > accessing the data.  A very common example is with the use of
> > optimistic vs pessimistic lock managers.  Some apps may be
> > read-only or read-mostly and the default optimistic lock
> > manager is more than sufficient.  While, other apps may be
> > heavier on the write processing and they may require a
> > pessimistic lock manager.
> >
> > There are many other cases where the multiple configurations
> > make sense.
> >
> > Of course, many of these configuration items can be
> > controlled from within your application as well, but if it's
> > a global configuration setting why not just set it in one
> > place and not complicate your code?
> >
> > You mentioned a concern about "divergent states of data"...
> > This is really an aspect of your application, not the use of
> > multiple persistence units.
> > As long as you are using the proper locking mechanism and
> > isolation levels when interacting with the database, it
> > doesn't matter if you are using one or several PU definitions.
> >
> > Good luck,
> > Kevin
> >
> > On Fri, May 18, 2012 at 1:28 AM, Boblitz John
> > <John.Boblitz@bertschi.com>wrote:
> >
> > >
> > >
> > > > -----Ursprüngliche Nachricht-----
> > > > Von: Boblitz John [mailto:John.Boblitz@BERTSCHI.com]
> > > > Gesendet: Montag, 14. Mai 2012 15:07
> > > > An: 'users@openjpa.apache.org'
> > > > Betreff: pro & contra of using Multiple Persistence Units
> > > >
> > > > Good Afternoon,
> > > >
> > > > I have been looking around the interwebs but can't seem
> > to find any
> > > > discussions regarding the advantages / disadvantages of using
> > > > multiple persistence units in a Java SE environment to
> > connect to a
> > > > single data source.
> > > >
> > > > Does anyone know of a good link?
> > > >
> > > > Also, any info/recomendations from the community would be
> > great ...
> > > >
> > > > A bit of Background:
> > > >
> > > > I am currently working on an application which splits it's
> > > > functionality across several services, mainly based on
> > the function
> > > > of the data (basic code tables, product data, employee data, etc
> > > > ...) and / or an sub-application (Invoicing, etc ...).
> > > >
> > > > Each of the services will obviously need to access data
> > from other
> > > > services, and it is currently designed that each service has it's
> > > > own Persistence Unit.  IOW, basic code tables are "managed" in
> > > > packaged service with it's own persistence
> > implementation/unit JAR.
> > > >
> > > > I am a bit concerned that the various PU's will end up with
> > > > divergent states of the data, unless they can somehow be
> > synchronized.
> > > >
> > > > So, what I'm looking for is any information to help me
> > decide how to
> > > > best configure the persistence unit(s).
> > > >
> > > >
> > > > Thanks & Best Regards
> > > >
> > > >
> > > > 
> > > >
> > > > John Boblitz
> > > >
> > > > ----
> > > >
> > > > Who is General Failure, and why is he reading my hard disk?
> > > >
> > > >
> > >
> > > One time push of my previous post, in the hopes that it was simply
> > > overseen.  I will not do so again.
> > >
> > > John
> >
>

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