Invocation Service and Local Maps

Question

Hi,
     I want to use an InvocationService to perform a filtered query on the local data of a node in a distributed cache scheme. A simple keySet or entrySet will not work in my case as I want to push out some additional processing to each node.
     I am mainly concered on how to perform the query on only the local data of each node (how to get the local map and query it). Do you have an example or documentation of how to this?
     Thanks in advance.
     Joey

Answer 1

Cameron, this is in reference to a more "hands on" query approach previously discussed.
     Joey, the most direct means of accessing locally-hosted partitioned data is to access the cache's backing map directly. Since the data may be stored in serialized form, you'll need to access the backing map's context to get converters to convert from serialized form to regular java objects. The following snippet does a simple aggregation, using direct backing map access (for demonstration purposes only, obviously an InvocableMap aggregator would be easier, more reliable and more efficient for this specific use case). Keep in mind that when using InvocableMap, rebalancing and server failure are handled automatically; when using this lower-level approach, you'll need to handle failure manually (for queries, this usually just means re-issuing the query).
     (This snippet is from a larger examples compilation, so will not compile as-is due to a few "utility" calls).
     EDIT: Looking at the code below, I should also mention that there are separate converters for the cache keys and the cache values (this example happens to not process the cache keys).
              package examples.invocationWithBackingMap;
         import com.tangosol.net.AbstractInvocable;
         import com.tangosol.net.CacheFactory;
         import com.tangosol.net.CacheService;
         import com.tangosol.net.DefaultConfigurableCacheFactory;
         import com.tangosol.net.InvocationService;
         import com.tangosol.net.Member;
         import com.tangosol.net.NamedCache;
         import com.tangosol.net.DistributedCacheService;
         import com.tangosol.util.Binary;
         import com.tangosol.util.Converter;
         import com.tangosol.util.Base;
         import util.TerminateAgent;
         import util.Util;
         import java.util.Iterator;
         import java.util.Map;
         import java.util.Set;
         public class Main
             extends Base
              * Usage:
              * <pre>
              * java examples.invocationWithBackingMap.Main cluster-size
              * </pre>
              * @param args      command-line arguments
             public static void main(String[] args)
                 NamedCache cache = CacheFactory.getCache(CACHENAME);
                 int callerId = CacheFactory.ensureCluster().getLocalMember().getId();
                 // use (and start) an invocation service
                 InvocationService isvc =
                     CacheFactory.getInvocationService(INVOCATION_SERVICE_NAME);
                 int cClusterMembers = Integer.parseInt(args[0]);
                 Util.waitForCacheNodes(cache, cClusterMembers);
                 Util.verifyClusterSize(cClusterMembers);
                 // populate the cache (blindly; overwrites are ignored)
                 for (int i=0; i<100; i++)
                     cache.put(new Integer(i), new Integer(i));
                 // send to the partition owners
                 Set members = ((DistributedCacheService)cache.getCacheService()).getStorageEnabledMembers();
                 System.out.println("Number of storage-enabled nodes: " + members.size());
                 Map map = isvc.query(new SummingAgent(callerId), members);
                 System.out.println(map.size() + " node(s) responded");
                 int totalSum = 0;
                 System.out.println("Total should be 4950 for sum(0..99)");
                 for (Iterator iter = map.entrySet().iterator(); iter.hasNext();)
                     Map.Entry entry  = (Map.Entry)iter.next();
                     Member member = (Member)entry.getKey();
                     Integer memberSum = (Integer)entry.getValue();
                     // null if member died; did not run the Invocation service
                     //  or threw exception during execution
                     if (memberSum != null)
                         System.out.println("Sum of values on member " + member.getId() +
                                            " is " + memberSum);
                         totalSum += memberSum.intValue();
                     else
                         System.out.println("No result from " + member.getId());
                 System.out.println("Total sum is " + totalSum);
                 System.out.println("Terminating remote cluster memebers...");
                 // shut down the other cluster members remotely
                 // this member should not be acting as a cache server
                 azzert(!members.contains(CacheFactory.ensureCluster().getLocalMember()));
                 isvc.execute(new TerminateAgent(), members, null);
                 // leave the cluster
                 CacheFactory.shutdown();
             public static class SummingAgent extends AbstractInvocable
                 public SummingAgent() {}
                 public SummingAgent(int callerId)
                     m_callerId = callerId;
                 public void run()
                     System.out.println("Running agent from member " + m_callerId + "...");
                     NamedCache cache = CacheFactory.getCache(CACHENAME);
                     CacheService service = cache.getCacheService();
                     DefaultConfigurableCacheFactory.Manager bmm =
                         (DefaultConfigurableCacheFactory.Manager)service.getBackingMapManager();
                     Map backingMap = bmm.getBackingMap(CACHENAME);
                     Converter valueConverter =
                         bmm.getContext().getValueFromInternalConverter();
                     int sum = 0;
                     // if concurrent updates are possible you need to deal with
                     // ConcurrentModificationException thrown by the iter.next() call
                     for (Iterator iter = backingMap.values().iterator();iter.hasNext();)
                         // data stored in Binary (wire) format
                         Binary binary = (Binary)iter.next();
                         Integer value = (Integer)valueConverter.convert(binary);
                         sum += value.intValue();
                     setResult(new Integer(sum));
                 protected int m_callerId;
             public static final String CACHENAME = "dist-InvocationWithBackingMap";
             public static final String INVOCATION_SERVICE_NAME="InvocationService";