@Override
    public ExtendedCell getKey() {
      byte[] key = new byte[current.keyLength];
      System.arraycopy(current.keyBuffer, 0, key, 0, current.keyLength);
      return new KeyValue.KeyOnlyKeyValue(key);
    }
Copies only the key part of the keybuffer by doing a deep copy and passes the seeker state
members for taking a clone. Note that the value byte[] part is still pointing to the
currentBuffer and represented by the valueOffset and valueLength
hbase-common/src/main/java/org/apache/hadoop/hbase/io/encoding/BufferedDataBlockEncoder.java