Cassandra supports applications of ours that are decoupled from our main application running on MySQL. For instance our machine learning team (see TechCrunch’s EyeEm’s Algorithms Are Learning What Makes A Photo Great) has the demand to store big amounts of data that is denormalised and does not directly need to be accessed from our core community product. Also we migrated big amounts of data, that we need to make more sense of our photos in our photo search, that is not directly coupled to and queried by our main community application and thus could easily migrated off of it in order to keep the main database small and agile. The part of our application indexing the photos into our search is easily able to fetch the needed denormalised data of Cassandra and we have less of an headache scaling our main database.
Cassandra gives us a resilient data storage, that allows operations to easily scale up and down based on usage. The CQL interface brought an easy migration path in terms of not having to relearn a query language and Cassandra supports us in not allowing schemas that would not scale on any database anyway.
There was a lot of documentation on various blogs and it was easy to find some guidance on twitter as well. That said, there wasn’t much support on the PHP side of things, that we needed for our main product.