public Frame getInvoke(RelNode r, RelNode parent) {
    final Frame frame = dispatcher.invoke(r);
    if (frame != null) {
      map.put(r, frame);
    }
    currentRel = parent;
    return frame;
  }
Rewrites a {@link Aggregate}.

@param rel Aggregate to rewrite
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRelDecorrelator.java