This stage was used for optimizing predicates of the shape {ts: {$gte: <Timestamp>}} on the oplog. However, its implementation was MMAP-specific. On WiredTiger systems, the ts of each oplog entry forms the RecordId for the WT table backing the oplog. The beginning of the oplog scan can be found efficiently by simply seeking to the appropriate RecordId.

Since MMAP is no longer supported, OplogStart can be removed.