Java.lang.ClassCastException when executing an AbstractAggregator

Question

I'm trying to run an agregator over a distributed cache and I'm getting this exception:
(Wrapped: Failed request execution for NPDistributedCache service on Member(Id=2, Timestamp=2013-03-16 09:46:09.907, Address=127.0.0.1:8090, MachineId=27728, Location=site:,machine:proto1,process:716)) java.lang.ClassCastException: com.tangosol.util.extractor.ReflectionExtractor cannot be cast to com.tangosol.util.InvocableMap$EntryAggregator
        at com.tangosol.util.Base.ensureRuntimeException(Base.java:288)
        at com.tangosol.coherence.component.util.daemon.queueProcessor.service.Grid.tagException(Grid.CDB:36)
        at com.tangosol.coherence.component.util.daemon.queueProcessor.service.grid.partitionedService.PartitionedCache.validateRequestForStorage(PartitionedCache.CDB:37)
        at com.tangosol.coherence.component.util.daemon.queueProcessor.service.grid.partitionedService.PartitionedCache.onAggregateFilterRequest(PartitionedCache.CDB:16)
        at com.tangosol.coherence.component.util.daemon.queueProcessor.service.grid.partitionedService.PartitionedCache$AggregateFilterRequest.run(PartitionedCache.CDB:1)
        at com.tangosol.coherence.component.net.message.requestMessage.DistributedCacheRequest.onReceived(DistributedCacheRequest.CDB:12)
        at com.tangosol.coherence.component.util.daemon.queueProcessor.service.Grid.onMessage(Grid.CDB:34)
        at com.tangosol.coherence.component.util.daemon.queueProcessor.service.Grid.onNotify(Grid.CDB:33)
        at com.tangosol.coherence.component.util.daemon.queueProcessor.service.grid.PartitionedService.onNotify(PartitionedService.CDB:3)
        at com.tangosol.coherence.component.util.daemon.queueProcessor.service.grid.partitionedService.PartitionedCache.onNotify(PartitionedCache.CDB:3)
        at com.tangosol.coherence.component.util.Daemon.run(Daemon.CDB:42)
        at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.ClassCastException: com.tangosol.util.extractor.ReflectionExtractor cannot be cast to com.tangosol.util.InvocableMap$EntryAggregator
        at com.tangosol.coherence.component.util.daemon.queueProcessor.service.grid.partitionedService.PartitionedCache$AggregateFilterRequest.read(PartitionedCache.CDB:7)
        at com.tangosol.coherence.component.util.daemon.queueProcessor.service.Grid.deserializeMessage(Grid.CDB:19)
        at com.tangosol.coherence.component.util.daemon.queueProcessor.service.Grid.onNotify(Grid.CDB:31)
        ... 4 moreThe agregator extends from the AbstractAgregator class and I'm using an IdentityExtractor. Here is a piece of code of the agregator:
public class MyAggregator extends AbstractAggregator {
    public MyAggregator() {
        // IdentityExtractor because I want the stored entry
        super(IdentityExtractor.INSTANCE);
    protected Object finalizeResult(boolean isFinal) {
        // Simple aggregation operation, with no interaction with the coherence env
    protected void init(boolean isFinal) {
     // Initialize aggregators vars   
    protected void process(Object value, boolean isFinal) {
        // Here we might access named caches using the cache factory to get entries related to the current one
        // i.e. If we are processing a product entry, we will go get from another cache the 'owner' (company entry)
}To execute the aggregator, I'm using the InvocableMap.aggregate() method from the NamedCache get from the CacheFactory.getCache(). As filter, I'm using a simple EqualsFilter("getClass", type).
All the caches that are used by this aggregator are cofigured using this schema (even those that are get within the process() method)
<near-scheme>
     <scheme-name>np-near</scheme-name>
     <front-scheme>
          <local-scheme/>
     </front-scheme>
     <back-scheme>
          <distributed-scheme>
               <scheme-name>np-distributed</scheme-name>
               <service-name>NPDistributedCache</service-name>
               <backup-count>2</backup-count>
               <backing-map-scheme>
                    <local-scheme>
                         <eviction-policy>LRU</eviction-policy>
                         <high-units>10000</high-units>
                    </local-scheme>
               </backing-map-scheme>
               <autostart>true</autostart>
          </distributed-scheme>
     </back-scheme>
     <autostart>true</autostart>
</near-scheme>
Why coherence is trying to cast an extractor to an Aggregator? Which coherence component is using a ReflectionExtractor in my scenario? IMO, I'm using the InvocableMap API to execute a simple aggregator with an IdentityExtractor. Maybe getting others entries within the process() method are causing this? And if it is the case: how can I get others related entries within an aggregator? (I know the problem of getting entries within a Processor (for edition), but for agregation (for read only) this should be feasible right?
Important info:
* We are using Coherence 3.7 with the development license and the idea is to deploy the application in production with the standard licence
* When there is only one single member in the cluster, the agregation works as expected.
Edited by: ggarciao.com on Mar 16, 2013 11:59 AM
Adding coherence version
Edited by: ggarciao.com on Mar 16, 2013 2:48 PM

Answer 1

Hi,
At the end of your post you say that when there is only a single member in the cluster that it works as expected so this could suggest you have a serialization issue. Do you have the same serializer configured everywhere? If you are using POF is the POF configuration correct and are the serializiation methods in your extractor correct?
Another point - it is not a good idea to access other caches using Cachefactory.getCache() from inside the aggregator's process method. This would cause re-entrant calls - i.e. calls from one worker thread in the cache service to another worker thread and can cause either thread starvation and in the worst case can cause your cluster to deadlock due to running out of worker threads.
You say in the code comments that the caches you want to get are to get related data - if you use key association to co-locate related data in other caches in the same cache service onto the same partition then there are more reliable and safer ways to get related data directly from the backing maps.
If you are going to go down the route of accessing other caches directly you need to be very careful about what services those other caches are in and what code you execute against those caches.
JK