@Override
  protected Optional<MajorCompactionRequest> getMajorCompactionRequest(RegionInfo hri)
    throws IOException {
    return MajorCompactionTTLRequest.newRequest(connection, hri, htd);
  }
This tool compacts a table's regions that are beyond it's TTL. It helps to save disk space and
regions become empty as a result of compaction.
hbase-server/src/main/java/org/apache/hadoop/hbase/util/compaction/MajorCompactorTTL.java