@Override
  public void shutdown() {
    LOG.info("Shutting down HeartbeatScheduler");
    scheduler.shutdownNow();
  }
Scheduler invoked by each processor for heartbeating to a row of the table.
Heartbeats every 5 seconds.
The row is determined by the job model version and processor id passed to the scheduler.
All time units are in SECONDS.
samza-azure/src/main/java/org/apache/samza/coordinator/scheduler/HeartbeatScheduler.java