[justaaron]

more like a scaling issue, as mongo is master-slave and a distributed horizontally scaled world can't live with such a bottleneck.

[merlynn]

Well that’s just a ridiculously uninformed statement. Of course mongodb scales horizontally. I can share many success stories of massive scale with mongodb.

[tracker1]

Depends on your deployment specifics and your requirements. I would say that a replica set of mongodb may be faster, but a sharded replica set in mongo may be slower than a local cluster of foundation with the document layer interface.