Cassandra vs Azure Cosmos DB

• Continuous availability: as a fully distributed database (no master nodes), we can update nodes with rolling restarts and accommodate minor outages without impacting our customer services.
• Linear scalability: for every unit of compute that you add, you get an equivalent unit of capacity. The same application can scale from a single developer's laptop to a web-scale service with billions of rows in a table.
• Amazing performance: if you design your data model correctly, bearing in mind the queries you need to answer, you can get answers in milliseconds.
• Time-series data: Cassandra excels at recording, processing, and retrieving time-series data. It's a simple matter to version everything and simply record what happens, rather than going back and editing things. Then, you can compute things from the recorded history.

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• Injects unstructured data at a very high speed.
• No real need for administrative work, it indexes everything on it's own.

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• Cassandra runs on the JVM and therefor may require a lot of GC tuning for read/write intensive applications.
• Requires manual periodic maintenance - for example it is recommended to run a cleanup on a regular basis.
• There are a lot of knobs and buttons to configure the system. For many cases the default configuration will be sufficient, but if its not - you will need significant ramp up on the inner workings of Cassandra in order to effectively tune it.

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• Cosmos DB can be very expensive if you're using it for scenarios that are better completed in regular old Azure Table Storage or Blob Storage, specifically if you put some thought into your partitioning schemes. No product is a good substitute for thoughtful system design.
• It would be helpful if I had some more insight into how many resources (DTUs) an individual query uses.
• The auto-indexing is great, but a little mysterious -- not usually an issue but it does require some intentional thought.

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• I have no experience with this but from the blogs and news what I believe is that in businesses where there is high demand for scalability, Cassandra is a good choice to go for.
• Since it works on CQL, it is quite familiar with SQL in understanding therefore it does not prevent a new employee to start in learning and having the Cassandra experience at an industrial level.

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• Azure Cosmos DB may be expensive on its own, but it was cheaper than increasing the size/power of our VMs running SQL Server instances enough to keep up with the volume and velocity of the unstructured data.
• We got the JSON data out of our SQL Servers and they quit tipping over.

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