@Override
        public R call(AggregateService instance) throws IOException {
          RpcController controller = new AggregationClientRpcController();
          CoprocessorRpcUtils.BlockingRpcCallback<AggregateResponse> rpcCallback =
            new CoprocessorRpcUtils.BlockingRpcCallback<>();
          instance.getMin(controller, requestArg, rpcCallback);
          AggregateResponse response = rpcCallback.get();
          if (controller.failed()) {
            throw new IOException(controller.errorText());
          }
          if (response.getFirstPartCount() > 0) {
            ByteString b = response.getFirstPart(0);
            Q q = getParsedGenericInstance(ci.getClass(), 3, b);
            return ci.getCellValueFromProto(q);
          }
          return null;
        }
It gives the minimum value of a column for a given column family for the given range. In case
qualifier is null, a min of all values for the given family is returned.
@param table table to scan.
@param ci    the user's ColumnInterpreter implementation
@param scan  the HBase scan object to use to read data from HBase
@return min val &lt;R&gt;
@throws Throwable The caller is supposed to handle the exception as they are thrown &amp;
                  propagated to it.
hbase-endpoint/src/main/java/org/apache/hadoop/hbase/client/coprocessor/AggregationClient.java