Notifications about external database changes

[philk]

Hello,

I am having a little trouble understanding how my EntityManager could be  
informed about changes to the database that were made by a 3rd Party  
program in another process. Is there any recommended way to reload/refresh  
the entities in the entity manager? I am currently using  
"eclipselink.refresh=true" as a query hint in my getResultList() calls.  
But once you forget that, you will not see external changes. Is there a  
way to globally turn of entity caching?

Also is there a "non-pull" way of getting notified about changes in tables  
 from outside? My application needs to monitor progress on orders and  
currently I am polling every 10 seconds to do a full entity update using a  
"select e from SendOrder e" query. Which is of course highly inefficient.  
I could use DB-triggers but they cannot be managed by JPA and are not  
available on every database.

Any ideas?

Thanks,
Phil
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[Sebastien Tardif-2]

A fast implementation compatible with caching is that your DB send to
your application a JMS invalidation message containing the table name +
PK modified, likely implemented using triggers. In Oracle DB, it's
relatively easy, because already supporting JMS. Then your application
can match entities by using the table name received.

This way you just have a small window of stale data, which you can
protect using optimistic locking.

-----Original Message-----
From: eclipselink-users-bounces@...
[mailto:eclipselink-users-bounces@...] On Behalf Of Philipp
Kursawe
Sent: Monday, June 08, 2009 4:14 PM
To: eclipselink-users@...
Subject: [eclipselink-users] Notifications about external database
changes

Hello,

I am having a little trouble understanding how my EntityManager could be

informed about changes to the database that were made by a 3rd Party  
program in another process. Is there any recommended way to
reload/refresh  
the entities in the entity manager? I am currently using  
"eclipselink.refresh=true" as a query hint in my getResultList() calls.

But once you forget that, you will not see external changes. Is there a

way to globally turn of entity caching?

Also is there a "non-pull" way of getting notified about changes in
tables  
 from outside? My application needs to monitor progress on orders and  
currently I am polling every 10 seconds to do a full entity update using
a  
"select e from SendOrder e" query. Which is of course highly
inefficient.  
I could use DB-triggers but they cannot be managed by JPA and are not  
available on every database.

Any ideas?

Thanks,
Phil
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eclipselink-users mailing list
eclipselink-users@...
https://dev.eclipse.org/mailman/listinfo/eclipselink-users
_______________________________________________
eclipselink-users mailing list
eclipselink-users@...
https://dev.eclipse.org/mailman/listinfo/eclipselink-users

[philk]

On Tue, 09 Jun 2009 02:33:52 +0200, Sebastien Tardif  
<stardif@...> wrote:

> A fast implementation compatible with caching is that your DB send to
> your application a JMS invalidation message containing the table name +
> PK modified, likely implemented using triggers. In Oracle DB, it's
> relatively easy, because already supporting JMS. Then your application
> can match entities by using the table name received.

How would I setup such JMS scenario? Which topics I would need to  
subscribe to?


Thanks, for any help,
Phil
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[James Sutherland]

You can disable the shared cache using the persistence.xml property,

"eclipselink.cache.shared.default"="false"

Trigger or specific database mechanism are the only way to get events from the database.  You could maintain a open/changed or change number column in your tables that the external application must update, so you can at least limit your polling query to filter on that column.

philk wrote:

Hello,

I am having a little trouble understanding how my EntityManager could be  
informed about changes to the database that were made by a 3rd Party  
program in another process. Is there any recommended way to reload/refresh  
the entities in the entity manager? I am currently using  
"eclipselink.refresh=true" as a query hint in my getResultList() calls.  
But once you forget that, you will not see external changes. Is there a  
way to globally turn of entity caching?

Also is there a "non-pull" way of getting notified about changes in tables  
 from outside? My application needs to monitor progress on orders and  
currently I am polling every 10 seconds to do a full entity update using a  
"select e from SendOrder e" query. Which is of course highly inefficient.  
I could use DB-triggers but they cannot be managed by JPA and are not  
available on every database.

Any ideas?

Thanks,
Phil