Cassandra: The Definitive Guide, 3rd Edition

Chapter 6. The Cassandra Architecture

3.2 Architecture—fundamental concepts or properties of a system in its environment embodied in its elements, relationships, and in the principles of its design and evolution.

ISO/IEC/IEEE 42010

In this chapter, we examine several aspects of Cassandra’s architecture in order to understand how it does its job. We’ll explain the topology of a cluster, and how nodes interact in a peer-to-peer design to maintain the health of the cluster and exchange data, using techniques like gossip, repair, hinted handoff, and lightweight transactions. Looking inside the design of a node, we examine architecture techniques Cassandra uses to support reading, writing, and deleting data, and examine how these choices affect architectural considerations such as scalability, durability, availability, manageability, and more. We’ll also learn about the data structures inside a node, including commit logs, memtables, caches, and SSTables.

As we introduce these topics, we also provide references to where you can find their implementations in the Cassandra source code.

Data Centers and Racks

Cassandra is frequently used in systems spanning physically separate locations. Cassandra provides two levels of grouping that are used to describe the topology of a cluster: data center and rack. A rack is a logical set of nodes in close proximity to each other, perhaps on physical machines in a single rack of equipment. A data center is a logical set of racks, perhaps located ...