There's nothing wrong with Cassandra but its reliability depends on settings you use. For example you should prefer using CRDTs. The article is a good guide to understand what's going on.

RedShift technically is a service for which you pay not a database (I did not use it but I believe it is Postgres - don't quote me on that), so if it doesn't provide what's promised you take it with Amazon.

Anyway the summarize databases. Currently we have two types:

- relational databases - old and proven, always consistent, but typically not distributed

- so called NoSQL which I think only worth attention are AP (from the CAP). These databases scale, but are eventually consistent. This means they are consistent most of the time, but not always. It's good for storing things that while important, it's acceptable when some individual entries are wrong or lost (user sessions, shopping carts, tracked information about users etc)

There are also databases like Mongo which are snake oil.