Robin Schumacher

<p><em>This is an excerpt from the DataStax whitepaper Data Modeling in Apache Cassandra™; which delves into how to choose the right data model for your Apache Cassandra™ application in 5 easy steps. <a href="https://www.datastax.com/resources/whitepaper/data-modeling-apache-cassandra">Click here</a> to download the full whitepaper.</em></p>

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<h2>Intro</h2>

<p>For web-scale applications, Apache Cassandra™ is a favorite choice among architects and developers.&nbsp;It offers many advantages including performance, scalability, continuous availability, geographic distribution, and ease of management.&nbsp;Today, Cassandra is among the most successful NoSQL databases.&nbsp;It is used in countless applications from online retail to internet portals to time-series databases to mobile application backends.</p>

<p>While Cassandra is powerful and easy to use, having a well-designed data model is essential to meeting application performance and scalability goals. In this paper, aimed at technical people experienced with relational databases, we discuss five useful steps to realizing a high-quality data model for your Cassandra application.</p>

<h2>How Cassandra Stores Data</h2>

<p>Understanding how Cassandra stores data is essential to developing a good data model. Readers wishing to get a better understanding of Cassandra’s internal architecture can read the DataStax Apache Cassandra™ Architecture whitepaper.</p>

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<p><br />
<a class="zdb-click2tweet-link" href="/resources/whitepapers/apache-cassandra-architecture">Apache Cassandra™ Architecture</a></p>

<h5 class="zdb-click2tweet-text">Read this white paper to learn how Cassandra was born, how it’s evolved, how it operates, and what DataStax Distribution of Apache Cassandra™ adds to the equation.</h5>
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<p>Cassandra clusters have multiple nodes running in local data centers or public clouds. Data is typically stored redundantly across nodes according to a configurable replication factor so that the database continues to operate even when nodes are down or unreachable.</p>

<p>Tables in Cassandra are much like RDBMS tables. Physical records in the table are spread across the cluster at a location determined by a partition key. The partition key is hashed to a 64-bit token that identifies the Cassandra node where data and replicas are stored.&nbsp;The Cassandra cluster is conceptually represented as a ring, as shown in Figure 1, where each cluster node is responsible for storing tokens in a range.</p>

<p>Queries that look up records based on the partition key are extremely fast because Cassandra can immediately determine the host holding required data using the partitioning function.&nbsp;Since clusters can potentially have hundreds or even thousands of nodes, Cassandra can handle many simultaneous queries because queries and data are distributed across cluster nodes.</p>

<p><img alt="How Cassandra Stores Data" data-entity-type="file" data-entity-uuid="d19e0f63-5040-49d1-aa30-044dfa140593" src="https://www.datastax.com/sites/default/files/inline-images/DMiAPp1image.png" /></p>

<p class="text-align-right"><em>Figure 1 -&nbsp; How Cassandra Stores Data</em></p>

<p>&nbsp;</p>

<p>Partition keys can be single columns or can be composed of multiple columns.&nbsp;Cassandra also supports clustering columns (discussed shortly) that control how data records are grouped and organized within each partition. Records in Cassandra are stored as lists of key-value pairs where the column name is the key.</p>

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<p><em>Thanks for reading this excerpt from the DataStax whitepaper Data Modeling in Apache Cassandra™; tune in next week when we'll release another excerpt or&nbsp;<a href="https://www.datastax.com/resources/whitepaper/data-modeling-apache-cassandra">click here</a>&nbsp;to download the full asset.</em></p>


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