The query flag OPLOG_REPLAY needs to be set when doing change notification queries, or the collection scan will have to search the entire oplog from the beginning whenever doing a change notification. We also need to make sure the query is of the proper form for oplog replay for both initial query and resume; this basically means there must be a timestamp "greater than" or "greater than or equal" term at the top level of the query; the system will invariant() if this is not the case.