long getWriteId() {
      return writeId;
    }
for reading "original" files - i.e. not native acid schema.  Default value of 0 is
appropriate for files that existed in a table before it was made transactional.  0 is the
primordial transaction.  For non-native files resulting from Load Data command, they
are located and base_x or delta_x_x and then writeId == x.
ql/src/java/org/apache/hadoop/hive/ql/io/orc/OrcRawRecordMerger.java