Cassandra: The Definitive Guide, 3rd Edition

Chapter 9. Writing and Reading Data

Now that you understand the data model and how to use a simple client, let’s dig deeper into the different kinds of queries you can perform in Cassandra to write and read data. We’ll also take a look behind the scenes to see how Cassandra handles your queries. Understanding these details will help you design queries that will perform well and provide the behavior you need.

As with the previous chapter, we’ve included code samples using the DataStax Java Driver to help illustrate how these concepts work in practice.

Writing

Let’s start by noting some basic properties of writing data to Cassandra. First, writing data is very fast in Cassandra, because its design does not require performing disk reads or seeks. The memtables and SSTables save Cassandra from having to perform these operations on writes, which slows down many databases. All writes to disk in Cassandra are append only.

Because of the database commit log and hinted handoff design, the database is always writable, and within a row, writes are always atomic.

Write Consistency Levels

Cassandra’s tuneable consistency levels mean that you can specify in your queries how much consistency you require on writes. A higher consistency level means that more replica nodes need to respond, indicating that the write has completed. Higher consistency levels also come with a reduction in availability, as more nodes must be operational for the write to succeed. The implications of using the different ...