GetStream's CTO and co-author of the stream-framework here. If anyone has any questions I will be more than happy to reply :)
Why did you decide to use Cassandra and in what areas are you using it?
We use Cassandra as main feed storage. We chose Cassandra over Redis (the other storage backend supported by stream-framework) because it was easier for us to operate it (scaling up/down servers, backups/restores ..) and because it has built-in support for multi datacenter deployments.
Why did you decide to use Redis and in what areas are you using it?
Thanks for the post on HN, author of the article here. Looking forward to feedback.