pager may purge an item before its expiration time if user sets a new expiration time for an already expired key

exp = 7 sec, exp_pager_stime=5 , vbucket = 0 . working set 4000 keys

first few iterations are okay but get fails more often in later iterations.

iteration 0 ok
iteration 1 ok
iteration 2 ok
iteration 3 ok
iteration 4 438 keys not_found
iteration 5 ok
iteration 6 ok
iteration 7 1232 keys not_found
iteration 8 ok
iteration 9 466 keys not_found
iteration 10 ok
iteration 11 ok
iteration 12 1320 keys not_found
iteration 13 ok
iteration 14 327 keys not_found
iteration 15 ok
iteration 16 ok
iteration 17 1503 keys not_found
iteration 18 ok
iteration 19 521 keys not_found
iteration 20 ok
iteration 21 ok
iteration 22 1660 keys not_found
iteration 23 ok
iteration 24 346 keys not_found
iteration 25 ok
iteration 26 ok
iteration 27 1682 keys not_found
iteration 28 ok
iteration 29 233 keys not_found
iteration 30 ok
iteration 31 ok
iteration 32 1565 keys not_found
iteration 33 ok
iteration 34 472 keys not_found
iteration 35 ok
iteration 36 ok


  while iteration < 50:
      start = time.time()
      for key in keys:
          mc.set(key, expiration, 0, payload, vbucket=0)
      for key in keys:
          try:
              a, b, c = mc.get(key, vbucket=0)
          except Exception as ex:
              print "unable to get key {0} in {1}th iteration because {2}".format(key, iteration, ex)
      iteration += 1
      delta = time.time() - start
      time.sleep(abs(expiration - delta))