@Override
    public synchronized void onRegionComplete(RegionInfo region, AggregateResponse resp) {
      try {
        aggregate(region, resp);
      } catch (IOException e) {
        completeExceptionally(e);
      }
    }
This client class is for invoking the aggregate functions deployed on the Region Server side via
the AggregateService. This class will implement the supporting functionality for
summing/processing the individual results obtained from the AggregateService for each region.
hbase-endpoint/src/main/java/org/apache/hadoop/hbase/client/coprocessor/AsyncAggregationClient.java