Reduce the number of accesses to consistent map

Stop accessing the consistent map when the resource is discrete.
Now, access to the consistent map happens only when the resource
is continuous.

Change-Id: Ic1cb1d94d32a2097dfca891e1d2de7fdc5d4c00a

@@ -202,10 +202,18 @@ public class ConsistentResourceStore extends AbstractStore<ResourceEvent, Resour
         TransactionalMap<ContinuousResourceId, ContinuousResourceAllocation> continuousConsumerTxMap =
                 tx.getTransactionalMap(CONTINUOUS_CONSUMER_MAP, SERIALIZER);
 
-        // Extract Discrete instances from resources
+        // Look up resources by resource IDs
         List<Resource> resources = ids.stream()
                 .filter(x -> x.parent().isPresent())
-                .flatMap(x -> Tools.stream(lookup(childTxMap, x)))
+                .map(x -> {
+                    // avoid access to consistent map in the case of discrete resource
+                    if (x instanceof DiscreteResourceId) {
+                        return Optional.of(Resources.discrete((DiscreteResourceId) x).resource());
+                    } else {
+                        return lookup(childTxMap, x);
+                    }
+                })
+                .flatMap(Tools::stream)
                 .collect(Collectors.toList());
         // the order is preserved by LinkedHashMap
         Map<DiscreteResourceId, List<Resource>> resourceMap = resources.stream()