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From Miłosz <mtyle...@o2.pl>
Subject Re: Re: no cache, direct reads from db each time..
Date Tue, 08 Jun 2010 20:17:02 GMT
Hi Nino,

Roughly speaking, the idea is that you implement some database-specific listener. The listener
is invoked when the data you are interested in changes. Until the listener is invoked, you
can use data from the cache. When the listener is invoked, you refresh the entities or execute
your query against the database.

As Pinaki has mentioned, one can imagine implementing a RemoteCommitProvider [1] which will
invalidate OpenJPA's cache when the data in database changes.

As for SQL Server, I remember reading about a change notification facility but it migth be
available only for .NET.

Cheers,
Milosz

[1] http://openjpa.apache.org/builds/2.0.0/apache-openjpa-2.0.0/docs/manual/manual.html#ref_guide_event


> Hmm it's either mysql or microsoft sql server... However if they
> supported that feature, how would you suggest I procedede.. Calling
> em.flush or? Anyhow I guess I could call em.flush, instead of
> refreshing every object retrieved from the em.
> 
> However calling it when it's only relevant would be a lot more performant..
> 
> 2010/6/7 Miłosz <mtylenda@o2.pl>:
> > Hi Nino,
> >
> > If you can stick to database-specific API, check whether your database supports
some sort of change propagation mechanism.
> >
> > Examples:
> > Oracle - Data Change Notification [1]
> > PostgreSQL - LISTEN/NOTIFY [2]
> >
> > Regards,
> > Milosz
> >
> > [1] http://www.oracle.com/technology/obe/11gr1_db/appdev/dcn/dcn.htm
> > [2] http://jdbc.postgresql.org/documentation/83/listennotify.html
> >
> >
> >
> >
> >> Hi
> >>
> >> I have a case where I need to check the database on each query,
> >> because there can be modifications to the data from a 3rd party non
> >> java application. Currently I have to refresh each object, otherwise
> >> it could be stale data however this approach are really slow and feels
> >> very wrong..
> >>
> >> Any ideas on what I could do?
> >>
> >> regards Nino
> >
> >


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