     multi.smembers @key('BLOCKED')
     multi.hlen @key('WORKERS')
     multi.exec (multi_err, multi_res) =>
-
       return callback multi_err if multi_err
 
       # Process the result of the transaction.

  
  # Statistics of a queue include:
  # 
  #   + `total`
  #     - `tasks`, total tasks placed
  #     - `groups`, total groups placed

  #     - `tasks`, total blocked tasks
  #   + `pending_tasks`, total pending tasks
  #
  # `statistics` is an asynchronous method. Arguments of the callback function
  # follow node.js async callback convention: `err` and `res`.
  #
  # Below is an example of the `res` object:
  #
  #       { name: 'task',
  #         total: { groups: 10, tasks: '20000' },
  #         finished_tasks: '8373',
  #         average_pending_time: 313481,
  #         average_processing_time: 14,
  #         blocked: { groups: 9, tasks: 11612 },
  #         processing_tasks: 0,
  #         failed_tasks: 15,
  #         workers: 1,
  #         pending_tasks: 0 }
  #
  # **Usage:**
  #
  #       queue.statistics (err, statistics) -> # YOUR CODE
  statistics: (callback) ->

    # Start a transaction, in the transaction:
