public void clear() throws IOException {
        valLenBuffer.reset();
        columnValBuffer.reset();
        prevValueLength = -1;
        runLength = 0;
      }
Write KeyBuffer/ValueBuffer pairs to a RCFile. RCFile's format is
compatible with SequenceFile's.
ql/src/java/org/apache/hadoop/hive/ql/io/RCFile.java