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Where is the distribution?  RSS feed

 
Maulin Vasavada
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Hi all,
I understand the part where it says J2EE is distributed as client can be anywhere and server can be anywhere as far as they are reachable to each other BUT is it possible to have one application deployed on multiple machines , hence multiple JVMs?
That would mean, there could be more than one Entitybean on different machines referring to one data in the database. How does appserver handles it? How would it synch b/w two objects? I have not read clustering so far but I would read if that is applicable here...
Please let me know if I my view is not correct.
Regards
Maulin
 
David Harkness
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As you've stated, clustering is one specific case of this (multiple application servers managing the same database data), and how it works depends on the application server involved. With WebLogic, for example, I believe that committing changes to an entity bean will result in replicated instances of that bean being invalidated in all other cluster nodes.
Another case is running two applications that make use of entity beans fronting the same database. In this case, I doubt *any* spplication servers will perform the above actions.
There are methods you can use to avoid problems. One is to use a version_num or timestamp column to enforce that you have the latest view of the bean. Another is to use JMS or some other mechanism to broadcast beans that should be invalidated.
 
Maulin Vasavada
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Hi David,
Thanks for the response. For now the case of two different application accessing the same bean is complicated for me to consider. So, I would ignore it I guess
In my application I don't think that would really happen.
Regards
Maulin
 
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