Right now, change stream will flatten out a transaction into individual operations, i.e., if we do two operations within a transaction, change stream will generate two events.

However there is no total ordering of the events that happens within the transaction. This is important if we do two updates on the same object within a transaction, since both operations share the same optime (clusterTime), there is no way to provide the ordering between these two events.

It would be helpful if we can provide an ordering number on every events from the same transaction for this purpose.