public List<ReduceSinkOperator> getBottomReduceSinkOperators() {
    return bottomReduceSinkOperators;
  }
IntraQueryCorrelation records a sub-tree of the query plan tree which can be
evaluated in a single MR job. The boundary of this sub-tree is recorded by
the ReduceSinkOperators the the bottom of this sub-tree.
Also, allReduceSinkOperators in IntraQueryCorrelation contains all
ReduceSinkOperators of this sub-tree.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/correlation/IntraQueryCorrelation.java