public ImmutableList<RexNode> getKeys() {
    return keys;
  }
Creates a HiveSortExchange.

@param input     Input relational expression
@param distribution Distribution specification
@param collation Collation specification
@param keys Keys specification
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/reloperators/HiveSortExchange.java