Is Cassandra suitable for a system that requires frequent queries (reads/writes)?

Question

I'm developing a web application that requires a lot of users to be in the same "universe", where a lot of frequent queries will happen:

• frequent lookups of clients that are in a certain box area (between X1, X2, Y1 and Y2)
• frequent position updates by clients
• frequent chat messages by clients
• frequent status updates by clients
• frequent connections and disconnections of new and old clients

I believe my nodes can have enough memory for all currently online users to be in RAM. This is why I originally considered Redis. However, I decided Redis is not applicable here because:

• it has a single point of failure (one master server)
• only the master server can write, if one has 40 nodes then 39 slaves would have to make the one master write each and every entry

Cassandra seems to solve these issues.

However, is Cassandra also suitable for my frequent queries?

Answer 1

Cassandra is definitely a superb solution for handling writes but if you can tell your read load then definitely you can expect a precise answer but generally reads are also good as long as you have enough RAM.

The user case you described seems to include many joins..

Do you have enough reasons to adopt NoSQL solution right from the developmental stage? Because Cassandra is basically a solution for setups which require high scalability BUT at the expense of de-normalization and sacrificing Joins to a good extent. In other words you need higher disk space but low CPU.

Or have you finalized your database design and apparent scheme (though Cassandra is not schema bound) which fulfills all of your query especially read query requirements? (its v.imp)

Answer 2

Cassandra optimises writes over reads (reads are expensive compared to writes), but it can still sustain high read and write throughput simultaneously.

With the right column family structures you should be able to do what you want at high frequencies, depending on how big your cluster is.

Personally I'd use Redis for caching most of the information, and only read from Cassandra on cache miss.