public boolean splittingAllowed() {
    JdbcRelVisitor visitor = new JdbcRelVisitor();
    visitor.go(getInput());
    return visitor.splittingAllowed;
  }
Whether the execution of the query below this jdbc converter
can be split by Hive.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/reloperators/jdbc/HiveJdbcConverter.java