> 1. What controls it? Is there some piece of gateway software that
negotiates
> where to go in the cluster?
This is totally vendor independant. In Sybase EAServer there is no single
server nor gateway that manages the cluster. Every server in the cluster
acts as a dispatcher across the cluster through the naming services.
>
> 2. IN a cluster, is there always only one instance of an entity bean
fora
> given row?
Again vendor dependant but in most cases no there is not. Actually to be
honest in most cases although there is only on EJBObject logical object,
there can be many instances even within a single server. Unless Im mistaken
I only know of BEA that creates justa single physical instance to represent
a single EJBObject.
>
> 3. If 2 is answered yes, doesn't this imply, since the EJB spec says
nothing
> about load balancing, that the spec and entity beans in general are
non-calable?
I dont see your connection here.
> That is, multiple clients uisng multipel appservers in a cluster still
need
> somehow to go to the same instance in one apps erver instance.
They do not. Each client gets a single EJBObject which can have many
physical instances. This does bring about some consistancy issues which
most vendors deal with by either passive solutions like optimistic locking,
or active solutiosn like distributed caches. Both solutions can deal with
logical diamonds as well.
Dave Wolf
Internet Applications Division
Sybase
That doesn't
> sound very scalable. In that case, clustering sounds pretty meaningfless,
and
> claimns that EJBs are scalable would seem not to apply to entity beans.
Am I
> missing something in this? Thanks.
>
>
> Ken
>
>
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