The reality is that not every transaction in every application requires full ACID guarantees, and ACID properties themselves can be viewed as more of a continuum where a given transaction might require different degrees of each property.
Cassandra's approach to availability takes this continuum into account. In contrast to its relational predecessors–and even most of its NoSQL contemporaries–its original architects considered availability as a key design objective, with the intent to achieve the elusive goal of 100 percent uptime. Cassandra provides numerous knobs that give the user highly granular control of the ACID properties, all with different trade-offs.
The remainder of this chapter offers an introduction to Cassandra's high availability attributes and features, with the rest of the book devoted to help you to make use of these in real-world applications.
