@Override
  public GetSchemaAlterStatusResponse getSchemaAlterStatus(RpcController controller,
    GetSchemaAlterStatusRequest req) throws ServiceException {
    // TODO: currently, we query using the table name on the client side. this
    // may overlap with other table operations or the table operation may
    // have completed before querying this API. We need to refactor to a
    // transaction system in the future to avoid these ambiguities.
    TableName tableName = ProtobufUtil.toTableName(req.getTableName());

    try {
      server.checkInitialized();
      Pair<Integer, Integer> pair = server.getAssignmentManager().getReopenStatus(tableName);
      GetSchemaAlterStatusResponse.Builder ret = GetSchemaAlterStatusResponse.newBuilder();
      ret.setYetToUpdateRegions(pair.getFirst());
      ret.setTotalRegions(pair.getSecond());
      return ret.build();
    } catch (IOException ioe) {
      throw new ServiceException(ioe);
    }
  }
Get the number of regions of the table that have been updated by the alter.
@return Pair indicating the number of regions updated Pair.getFirst is the regions that are yet
        to be updated Pair.getSecond is the total number of regions of the table
hbase-server/src/main/java/org/apache/hadoop/hbase/master/MasterRpcServices.java