[avital]

I believe this is solved by Mongo's "snapshot" method on cursors: https://docs.mongodb.com/v3.0/faq/developers/#faq-developers...

[glasser]

If I understand correctly, this method says "only scan the built in _id index, not any other index". Which means that you will not hit this index-specific bad behavior, but also that you won't get the performance characteristics of using an index.