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From Andrus Adamchik <>
Subject Re: Stateless server (GWT)
Date Wed, 27 Aug 2008 12:22:50 GMT
Hi Krzysztof,

You can switch to Cayenne 3.0M5. It uses weak references and will  
prevent objects in the ObjectStore from accumulating. Or throw away  
the context at the end of the request or after N requests.


On Aug 27, 2008, at 2:23 PM, Krzysztof Janowicz wrote:

> Hi,
> I am playing around with GWT, trying to implement a stateful client  
> with
> a stateless server (IMO this is the paradigm shift proposed by the
> google guys). While this is a very promising solution for massive Web
> 2.0 ajax applications, I am running into some trouble handling this  
> with
> cayenne (2.0.4).
> Most of the application logic is handled by the GWT client. The  
> servlet
> (GWT RPCService) is only used if the users change their settings or  
> have
> to interact with each other. As there will be many users I don't  
> want to
> have a session and associated datacontext per user. This would be very
> ineffective, since communication between client and server is  
> reduced to
> a minimum. In addition, the datacontext stores objects in the
> objectstore to manage their states, this is not necessary in a  
> stateless
> server scenario. Moreover, there are several isolated RPC services the
> users are interacting with.
> Hence, I decided to bind the context to a thread (see
> Each
> servlet handles a couple of threads automatically (in my case tomcat)
> and each thread has an own datacontext. This seems to be a nice  
> solution
> as I don't face and tread-safety problems and don't need to care about
> sessions.
> The first thing when executing a method within a RPCService is to  
> call a
> getcontext() method which gets the datacontext bounded to the thread
> (DataContext.getThreadDataContext()) or creates one
> (DataContext 
> .bindThreadDataContext(DataContext.createDataContext(false)))
> if this is the first time this thread is executed by the servlet
> container.  My only concern so far is the objectstore of the  
> datacontext
> which keeps collecting objects. I set  
> cayenne.DataRowStore.snapshot.size
> to 1 but this only affects the DataRowStore. I tried to use
> context.getObjectStore().startTrackingNewObjects() and then
> context.getObjectStore().unregisterNewObjects() every time i get the
> context from the thread but this does not solve my problem. IMO i  
> don't
> need to track any objects in the objectStore. If a client calls a
> RPCService to create/change/delete something, this is either directly
> commited to the DB (context.commitChanges()) or rolled back in case of
> an error (context.rollbackChanges()). As the datacontext is kept per
> thread its objectstore will run full of data which will probably be
> never used again. Is there a way to clear the objectstore (expect
> calling unregisterNode() for each created object by hand)? Should I
> create a new datacontext for a thread after a while?
> Any ideas? Thanks in advance.
> Krzysztof

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