docs: def commit(self, frame):
          """
          Handles COMMIT command: Commits specified transaction.
          """
          if not frame.transaction:
              raise ProtocolError("Missing transaction for COMMIT command.")
  
          if not frame.transaction in self.engine.transactions:
              raise ProtocolError("Invalid transaction: %s" % frame.transaction)
  
          for tframe in self.engine.transactions[frame.transaction]:
              del tframe.headers['transaction']
              self.process_frame(tframe)
  
          self.engine.queue_manager.clear_transaction_frames(
              self.engine.connection, frame.transaction)
          del self.engine.transactions[frame.transaction]