Spectrum of Consistency Models

What is consistency?

A consistency model specifies which results clients may observe when operations overlap or data is replicated. It lets you reason about reads and writes without treating every physical copy as if it changed at the same instant.

Before using a storage service such as S3 or Cassandra, identify the guarantees of the particular operation and configuration. The models below offer different ordering and visibility guarantees; the illustration is a learning aid rather than an exhaustive ranking of every consistency model.

The lesson compares eventual, causal, sequential, and linearizable behavior.

Various consistency models lie between these two ends, as shown in the illustration below: