Scaling has a number of components to it - it's not just about the absolute number of requests. There are always trade-offs (read up about the CAP theorem). My

Scaling has a number of components to it - it's not just about the absolute number of requests. There are always trade-offs (read up about the CAP theorem). My experience with Mongo has been that it has very inconsistent performance. Such inconsistency makes capacity planning very difficult. Also - stuff like failover, sharding etc. are not elegant.