def sync
      begin
        @f.flush
        @f.fsync
      rescue IOError => e
        PEROBS.log.fatal "Cannot sync flat file database: #{e.message}"
      end
      @index.sync
      @space_list.sync
    end
def sync
      begin
        @f.flush
        @f.fsync
      rescue IOError => e
        PEROBS.log.fatal "Cannot sync flat file database: #{e.message}"
      end
      @index.sync
      @space_list.sync
    end
Force outstanding data to be written to the filesystem.