My company made the same switch from MongoDB to Cassandra, a little over a year ago. We were storing analytics counters in Mongo and wanted better consistency

My company made the same switch from MongoDB to Cassandra, a little over a year ago. We were storing analytics counters in Mongo and wanted better consistency guarantees. What we found when we switched was that Cassandra had better consistency with similar performance to MongoDB. Then a few months later, as we accumulated more data, performance started to take a nosedive. Counter increments began impacting other database operations and the nodes would become unresponsive. Eventually we moved all of the counters to an in-memory aggregator that flushed to Postgres a couple of times a second. Counters were introduced in 0.8 (when we started using them) and are pretty half-baked. There has been some good discussion about overhauling counters, though I'm not sure when they're scheduled to land.