@Override
    public void remove() {
      // nothing to do
    }
A KeyValuesReader implementation that returns a sorted stream of key-values
by doing a sorted merge of the key-value in LogicalInputs.
Tags are in the last byte of the key, so no special handling for tags is required.
Uses a priority queue to pick the KeyValuesReader of the input that is next in
sort order.
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/tools/KeyValuesInputMerger.java