[tracker1]

I've mostly used MongoDB in mostly-read, and in a replica set... that said, if I needed to support pure scale, I'd be more inclined to reach for Cassandra. If I only needed mid-range replication, I'm more inclined to look at RethinkDB or ElasticSearch at this point. In fact the project I'm working on now is using ElasticSearch.

All of that said, you have to take a research paper funded by a database company (Datastax is backing Cassandra) with a grain of salt. Not to mention, that most people reach for MongoDB because it has some flexibility, and is a natural fit for many programming models. Beyond this, setting up a replica set with MongoDB was far easier than with any other database I've had to do the same with... Though I'd say getting setup with RethinkDB is nicer, but there's no automated failover option yet.

[takeda]

The results are so vastly apart than I don't think there's enough salt that you can add to make MongoDB look good here.

They also were quite generous by comparing load using non-durable write for CouchDB, HBase and MongoDB against Cassandra's durable write.

From my personal experience many scaling problems that you have with MongoDB once you switch even to a relational database that can't scale out are laughable.