Following is the tail of scheduler log after shutdown request received:

01/19 09:35:07.478 INFO |        monitor_db:0204| Shutdown request received.
01/19 09:35:07.479 WARNI|        base_utils:0862| (4, 'Interrupted system call')
01/19 09:35:07.480 CRITI|            drones:0097| Invalid response:
---

---
01/19 09:35:07.487 ERROR|     email_manager:0082| Uncaught exception; terminating monitor_db
Traceback (most recent call last):
  File "/usr/local/autotest/scheduler/monitor_db.py", line 180, in main_without_exception_handling
    dispatcher.tick()
  File "/usr/local/autotest/site-packages/chromite/lib/metrics.py", line 274, in wrapper
    return fn(*args, **kwargs)
  File "/usr/local/autotest/scheduler/monitor_db.py", line 398, in tick
    metrics.Counter('chromeos/autotest/scheduler/tick').increment()
  File "/usr/local/autotest/site-packages/chromite/lib/metrics.py", line 334, in __exit__
    outer_timer.add(self._total_time_s, fields=self._fields)
  File "/usr/local/autotest/site-packages/chromite/lib/metrics.py", line 68, in enqueue
    reset_after=self.reset_after))
  File "<string>", line 2, in put
  File "/usr/lib/python2.7/multiprocessing/managers.py", line 759, in _callmethod
    kind, result = conn.recv()
IOError: [Errno 104] Connection reset by peer
01/19 09:35:07.488 ERROR|     email_manager:0054| monitor_db exception
EXCEPTION: Uncaught exception; terminating monitor_db
Traceback (most recent call last):
  File "/usr/local/autotest/scheduler/monitor_db.py", line 180, in main_without_exception_handling
    dispatcher.tick()
  File "/usr/local/autotest/site-packages/chromite/lib/metrics.py", line 274, in wrapper
    return fn(*args, **kwargs)
  File "/usr/local/autotest/scheduler/monitor_db.py", line 398, in tick
    metrics.Counter('chromeos/autotest/scheduler/tick').increment()
  File "/usr/local/autotest/site-packages/chromite/lib/metrics.py", line 334, in __exit__
    outer_timer.add(self._total_time_s, fields=self._fields)
  File "/usr/local/autotest/site-packages/chromite/lib/metrics.py", line 68, in enqueue
    reset_after=self.reset_after))
  File "<string>", line 2, in put
  File "/usr/lib/python2.7/multiprocessing/managers.py", line 759, in _callmethod
    kind, result = conn.recv()
IOError: [Errno 104] Connection reset by peer

01/19 09:35:07.489 ERROR|        monitor_db:0100| Exception escaping in monitor_db
Traceback (most recent call last):
  File "/usr/local/autotest/scheduler/monitor_db.py", line 96, in main
    main_without_exception_handling()
  File "/usr/local/autotest/scheduler/monitor_db.py", line 192, in main_without_exception_handling
    "Uncaught exception; terminating monitor_db")
  File "/usr/lib/python2.7/contextlib.py", line 24, in __exit__
    self.gen.next()
  File "/usr/local/autotest/site-packages/chromite/lib/ts_mon_config.py", line 149, in _CreateTsMonFlushingProcess
    message_q.put(None)
  File "<string>", line 2, in put
  File "/usr/lib/python2.7/multiprocessing/managers.py", line 758, in _callmethod
    conn.send((self._id, methodname, args, kwds))
IOError: [Errno 32] Broken pipe

It took almost 4 mins before the scheduler is able to be restarted.