Chuck Butkus wrote:
>
> Does PCA provide fault tolerance over multiple machines transparently (to
> the servlets)?
>
> We were looking at using an Entity Bean to store info to an in memory object
> (where we would provide the replication) or to an OODBMS.
>
> Although the idea of eliminating the Entity Bean makes sense from a
> performance perspective.
>
> It seems to me that this is a significant hole in the EJB specification.
> Shouldn't there be a third type of bean (a "control" bean??) to handle
> multiple concurrent client access in memory AND provide scalability and
> fault tolerance. It seems like a common scenario to need have one logical
> component "instance" provided as many synchronized, distributed "physical"
> component instances without the need to explicitly store the data to a
> database to provide the synchronization. It would be nice to not have to
> look outside of the EJB container (i.e to PCA or other OODMSes) to get this
> functionality.
It is the job of the EJB container and resource managers to provide the
plumbing needed to effectively implement sharing and fault resilence of
entity state. The degree to which they do this is optional - some will
provide sophisticated object caching and high availability features and
others will provide none.
The EJB Entity Model provides the leverage to do this by either giving
the container direct control of the state (CMP) or by giving a DB
control of the state (BMP).
One of the fundamental goals of EJB is to eliminate the need for
developers to write this kind of code themselves.
An effective way to write a service that provides shared access to
cached data is to write it as a normal CMP entity and run it on a
container that provides the level of caching and fail-over that's
needed. All entities and their containers can also leverage the caching
and fail-over facilities provided by DB vendors.
>
> Anyone else have this issue/agree/disagree?? Any comment from anyone from
> Sun on this issue?
>
> Thanks,
> Chuck
>
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