mongodump improved behavior with --oplog

mongodump --oplog -vvvvv

2017-07-05T15:21:29.580-0400	found databases: local, test

2017-07-05T15:21:29.580-0400	enqueued collection 'test.c'

2017-07-05T15:21:29.581-0400	determined cluster to be a replica set

2017-07-05T15:21:29.581-0400	oplog located in local.oplog.rs

2017-07-05T15:21:29.581-0400	dump phase I: metadata, indexes, users, roles, version

2017-07-05T15:21:29.581-0400		reading indexes for `test.c`

2017-07-05T15:21:29.582-0400	determined cluster to be a replica set

2017-07-05T15:21:29.582-0400	oplog located in local.oplog.rs

2017-07-05T15:21:29.582-0400	getting most recent oplog timestamp

2017-07-05T15:21:29.582-0400	dump phase II: regular collections

2017-07-05T15:21:29.582-0400	finalizing intent manager with longest task first prioritizer

2017-07-05T15:21:29.582-0400	dumping up to 2 collections in parallel

2017-07-05T15:21:29.582-0400	starting dump routine with id=1

2017-07-05T15:21:29.582-0400	will listen for SIGTERM, SIGINT and SIGHUP

2017-07-05T15:21:29.582-0400	starting dump routine with id=0

2017-07-05T15:21:29.582-0400	ending dump routine with id=0, no more work to do

2017-07-05T15:21:29.586-0400	writing test.c to

2017-07-05T15:21:29.586-0400	counted 1422452 documents in test.c

2017-07-05T15:21:32.582-0400	[######################..]  test.c  1351210/1422452  (95.0%)

2017-07-05T15:21:32.664-0400	[########################]  test.c  1432268/1422452  (100.7%)

2017-07-05T15:21:32.664-0400	done dumping test.c (1432268 documents)

2017-07-05T15:21:32.666-0400	ending dump routine with id=1, no more work to do

2017-07-05T15:21:32.666-0400	dump phase III: the oplog

2017-07-05T15:21:32.666-0400	checking if oplog entry 6439369257720481699 still exists

2017-07-05T15:21:32.883-0400	oldest oplog entry has timestamp 6439369262015447267

2017-07-05T15:21:32.883-0400	oldest oplog entry of timestamp 6439369262015447267 is older than 6439369257720481699

2017-07-05T15:21:32.883-0400	Failed: oplog overflow: mongodump was unable to capture all new oplog entries during execution