private static boolean isHMasterWAL(Path path) {
    String fn = path.getName();
    return fn.startsWith(WALProcedureStore.LOG_PREFIX)
      || fn.endsWith(MasterRegionFactory.ARCHIVED_WAL_SUFFIX);
  }
Calculates the timestamp boundary up to which all backup roots have already included the WAL.
I.e. WALs with a lower (= older) or equal timestamp are no longer needed for future incremental
backups.
hbase-backup/src/main/java/org/apache/hadoop/hbase/backup/master/BackupLogCleaner.java