code: @Service
      public String requeueSweep(String workflowId) {
          boolean pushed = queueDAO.pushIfNotExists(WorkflowExecutor.DECIDER_QUEUE, workflowId, config.getSweepFrequency());
          return pushed + "." + workflowId;
      }
docs: Queue up all the running workflows for sweep.
  
  @param workflowId Id of the workflow
  @return the id of the workflow instance that can be use for tracking.