code: private void deleteBackups() {
          File[] storeDirList = ReadOnlyUtils.getVersionDirs(storeDir, 0L, getCurrentVersionId());
          if(storeDirList != null && storeDirList.length > (numBackups + 1)) {
              // delete ALL old directories asynchronously
              File[] extraBackups = ReadOnlyUtils.findKthVersionedDir(storeDirList,
                                                                      0,
                                                                      storeDirList.length
                                                                              - (numBackups + 1) - 1);
              if(extraBackups != null) {
                  for(File backUpFile: extraBackups) {
                      deleteAsync(backUpFile);
                  }
              }
          }
      }
docs: Delete all backups asynchronously