@Override
  protected Set<String> getStoresRequiringCompaction(MajorCompactionRequest request)
    throws IOException {
    return ((MajorCompactionTTLRequest) request).getStoresRequiringCompaction(htd).keySet();
  }
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