Major - P3 At log level 5, plus additional debug messages on entry to and exit from _waitForMajority, we see 3 WT transactions (536, 537, 538) begun and commited for the 3 documents deleted, but then an additional WT transaction (540) is created and remains open while _waitForMajority is called, and then is rolled back.
2017-08-02T16:48:48.562-0400 I SHARDING [RangeDeleter] Deleter starting delete for: test.c from { _id: MinKey } -> { _id: MaxKey }, with opId: 358 2017-08-02T16:48:48.562-0400 D SHARDING [RangeDeleter] begin removal of { : MinKey } to { : MaxKey } in test.c with write concern: { w: 1, j: false, wtimeout: 0 } 2017-08-02T16:48:48.562-0400 D STORAGE [RangeDeleter] WT begin_transaction for snapshot id 536 2017-08-02T16:48:48.563-0400 D STORAGE [RangeDeleter] WT commit_transaction for snapshot id 536 2017-08-02T16:48:48.563-0400 D STORAGE [RangeDeleter] WT begin_transaction for snapshot id 537 2017-08-02T16:48:48.563-0400 D STORAGE [RangeDeleter] WT commit_transaction for snapshot id 537 2017-08-02T16:48:48.563-0400 D STORAGE [RangeDeleter] WT begin_transaction for snapshot id 538 2017-08-02T16:48:48.563-0400 D STORAGE [RangeDeleter] WT commit_transaction for snapshot id 538 2017-08-02T16:48:48.563-0400 D STORAGE [RangeDeleter] WT begin_transaction for snapshot id 540 2017-08-02T16:48:48.563-0400 D SHARDING [RangeDeleter] end removal of { : MinKey } to { : MaxKey } in test.c (took 0ms) 2017-08-02T16:48:48.563-0400 I SHARDING [RangeDeleter] rangeDeleter deleted 3 documents for test.c from { _id: MinKey } -> { _id: MaxKey } 2017-08-02T16:48:48.563-0400 I SHARDING [RangeDeleter] xxx enter _waitForMajority 2017-08-02T16:48:48.580-0400 I SHARDING [RangeDeleter] xxx exit _waitForMajority 2017-08-02T16:48:48.580-0400 D STORAGE [RangeDeleter] WT rollback_transaction for snapshot id 540
This can result in a very long running transaction if there is replication lag, which can result in the instance getting stuck with a full cache, and that can result in a stall of as much as an hour until the _waitForMajority times out.