public void set(byte[] bytes, int offset) {
    externalBytes = bytes;
    this.offset = offset;
    bytesEmpty = false;
    currentBytes = externalBytes;

    clearTimestamp();
  }
true if data is stored in timestamp field rather than byte arrays.
     allows for lazy conversion to bytes when necessary
false otherwise
serde/src/java/org/apache/hadoop/hive/serde2/io/TimestampWritableV2.java