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From Michael Dick <>
Subject Re: Monitoring a database table or individual record for changes?
Date Thu, 11 Jun 2009 02:34:43 GMT
Hi Pablito,

I know this isn't exactly what you asked for but if you're using the same
database instance and the same PersistenceUnit then it might be easier to
use a L2 DataCache [1].

The L2 cache can be shared between all EntityManagers created by a single
EntityManagerFactory (or PersistenceUnit). There are also ways to keep the
cache synchronized if it's running on different JVMs (the manual is a good
starting point for that).


If you want to be notified to act on the changes (not just to make sure you
have the most up to date changes) then you'll need a callback like you
suggested. Sadly I'm not aware of such a callback in OpenJPA. Others on the
list might know though.

Hope this helps and let us know if you have other questions,

On Wed, Jun 10, 2009 at 4:26 PM, pablito <> wrote:

> Hi:
> I apologise for the newb question, but I'm a still a bit inexperienced when
> it comes to the database scene. Basically, I expect to have a number of
> servlets using a same database instance (under MySql if that matters). Is
> there any way to register a callback against a table or even a particular
> record for changes? Basically, I'm looking at a scenario where different
> servlets (in Tomcat) are interested in the same table/record and need to
> know to re-read the data when it changes.
> I ask here as we will be using OpenJpa, but I can't say I'm aware if
> databases generally have this capability. To be clear, I've looked at the
> Lifecycle callbacks, but I'm assuming that this isn't meant to cut across
> process boundaries. I'm just looking for confirmation either way.
> Many thanks,
> Pab
> --
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