[jboss-as7-dev] Clustered invocation design

[Scott Marlow]

On 11/21/2011 03:50 PM, David M. Lloyd wrote:
> On 11/21/2011 02:40 PM, Scott Marlow wrote:
>>>
>>> Summary
>>> -------
>>>
>>> For both options, we have to determine an appropriate load-balancing
>>> strategy. The choice of direction will affect how our clustering and
>>> transaction interceptors function. We also have to suss out the logic
>>> around dealing with conflicting or wrongly-ordered topology updates;
>>> hopefully our existing policies will continue to apply.
>>>
>>
>> I just wanted to mention, that when we talk about load-balancing
>> strategies/policies, that we might need some strategies that can handle
>> affinity for groups derived from extended persistence. In other words,
>> this would be a policy that understands how to migrate a group of
>> stateful session beans to the same target node, during fail-over.
>>
>> A simple example would be for two stateful session beans (SFSB1 +
>> SFSB2), that share an extended persistence context (XPC1). When an
>> instance of SFSB1 fails-over to a new cluster node, the corresponding
>> SFSB2 instance should fail-over to the same target node.
>>
>> Another example, would be the same as above, except SFSB2 has a
>> reference to SFSB3, which has a different XPC3. XPC3 is also used by
>> SFSB4. So, the load balancing policy would be need to have some
>> heuristic or maybe group-id that covers this case.
>>
>> One reason for ensuring that the same node is chosen for groups derived
>> from use of extended persistence context, is so that applications can
>> continue to see dirty data that is associated with the XPC.
>
> I'm going to move this out of the "clustered invocation" column and into
> the "stateful session replication" category which is, to my
> understanding, Paul's purview at the moment.

Just to keep everything in the open, I think when we do cluster extended 
persistence contexts, we will need a way to ensure that stateful session 
beans that are related (direct or indirectly) through extended 
persistence context inheritance, will need to fail-over as a group in 
the cluster.  If we come up with a load balancing policy that covers 
that magically, that would be cool.  I'll add more details on the "EJB 
passivation/activation, clustering and JPA extended persistence context 
handling..." thread...