public VectorAggregationBufferRow[] getAggregationBuffers() {
    return aggregationBuffers;
  }
the array of aggregation buffers for the current batch.
content past the {@link #getDistinctBufferSetCount()} index
is stale from previous batches.
@return
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/VectorAggregationBufferBatch.java