@Override
    public long applyAsLong(HStoreFile sf) {
      return sf.getMaximumTimestamp().orElse(Long.MAX_VALUE);
    }
Comparator for time-aware compaction. SeqId is still the first ordering criterion to maintain
MVCC.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreFileComparators.java