private static long getOldestToCompact(long maxAgeMillis, long now) {
    try {
      return LongMath.checkedSubtract(now, maxAgeMillis);
    } catch (ArithmeticException ae) {
      LOG.warn("Value for " + CompactionConfiguration.DATE_TIERED_MAX_AGE_MILLIS_KEY + ": "
        + maxAgeMillis + ". All the files will be eligible for minor compaction.");
      return Long.MIN_VALUE;
    }
  }
Returns a list of boundaries for multiple compaction output from minTimestamp to maxTimestamp.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/compactions/DateTieredCompactionPolicy.java