@Override
    public String toString() {
      MoreObjects.ToStringHelper stringHelper = MoreObjects.toStringHelper(this);
      if (isExpireByTimestampRange()) {
        stringHelper.add("fromTimestampMillis", fromTimestampMillis).add("toTimestampMillis", timestampMillis);
      } else if (isExpireByIds()) {
        stringHelper.add("idsToExpire", Arrays.toString(idsToExpire));
      } else if (isExpireByRetainLast()) {
        stringHelper.add("numRetainLast", numRetainLast);
      } else {
        stringHelper.add("timestampMillis", timestampMillis);
      }
      return stringHelper.toString();
    }
Value object class, that stores the expire snapshot operation specific parameters
<ul>
  <li>Expire snapshot value: it should be a timestamp in milliseconds</li>
</ul>
ql/src/java/org/apache/hadoop/hive/ql/parse/AlterTableExecuteSpec.java