       # Process the result of the transaction.
       #
       # 1. Process `STATISTICS` hash:
-      #
-      #     + Convert:
-      #       - `total_pending_time`, and `total_processing_time` into:
-      #       - `average_pending_time`, and `average_processing_time`
-      #     + Calibrate initial condition (in case of no task is finished).
-      #
+      #   + Convert:
+      #     - `total_pending_time`, and `total_processing_time` into:
+      #     - `average_pending_time`, and `average_processing_time`
+      #   + Calibrate initial condition (in case of no task is finished).
       # 2. Set `failed` key of returned object.
       statistics = multi_res[0] or {}
       result =

      @errors = []

    @handler task..., (err, res) =>
      finish_time  = Date.now()
      process_time = finish_time - start_time
      if err

        # Keep the error message for further inspection.

            # track tasks take the longest time processing in
            # `longest:task_name` sorted set.
            if not err
              finish_time  = Date.now()
              process_time = finish_time - start_time
              @redis.hincrby @key('STATISTICS'), 'finished', 1
              @redis.hincrby @key('STATISTICS'), 'total_pending_time', start_time - @queued_time
              @redis.hincrby @key('STATISTICS'), 'total_processing_time', process_time
