What is Cassandra?

• Distributed Database
• Open Source
• No single point of failure
• Highly Scalable
• Tunable Consistency

Why pick Cassandra?

• High availability
• Store massive amounts of data
• Handle high volume of reads or writes
• Easily integrate with analytics/search/etc

Who uses Cassandra?

Tons of people... some have listed themselves here:

http://planetcassandra.org/companies/

• Netflix
• Microsoft
• CERN
• NASA
• Instagram
• Call of Duty
• ... TONS more.....

How does it work?

• This is a cluster
• composed of peer-to-peer nodes (the dots)
• A "node" is an instance of Cassandra
• The "ring" is a range of token values from -2^63 to 2^63
• (out of scope: racks, data centers)

Change the Cluster

->

Change the Cluster

Cool Bits

• "Seed nodes" are just regular nodes that you (the ops person) knows about.
• No "special" node
• The topology and node liveliness are determined via gossip protocol, not a central authority.

Read/Write

Coordinator

• Client picks *any* node to talk to
• Any node can be a coordinator
• If a node goes down, just move on to the next one.

Write Replication

Writes can be Replicated

• The number of nodes that store a write is called the Replication Factor "RF"  
• You can write to every node in a cluster.
• You can control where writes are stored with a replication strategy.

Client Consistency

Cassandra offers tunable consistency

• CL is the number of nodes that must acknowledge a client request.
• Varying CL helps achieve differing availability or performance goals.
• Common CLs: 1, Quorum, ALL

Learn More

https://academy.datastax.com/