Actually, there is a lot of difference but not just because of the global lock to database lock transition. There is also a lot of work done on yield-before-loc

Actually, there is a lot of difference but not just because of the global lock to database lock transition. There is also a lot of work done on yield-before-lock: http://blog.serverdensity.com/goodbye-global-lock-mongodb-2-0-vs-2-2/ http://blog.serverdensity.com/goodbye-global-lock-mongodb-2-... And don't forget that replication also happens in a different database...