Cassandra vs Google Cloud Spanner: What are the differences?

Introduction: Cassandra and Google Cloud Spanner are both widely used and powerful distributed database systems. However, they differ in several key aspects. This article aims to highlight the key differences between Cassandra and Google Cloud Spanner.

1. Data Model: Cassandra is a NoSQL database that follows a columnar data model, while Google Cloud Spanner is a globally distributed relational database with support for strong consistency. This means Cassandra is schema-less and allows flexible data modeling, while Spanner enforces a relational model with schemas and relationships between tables.

2. Scalability: Cassandra is designed for massive scalability and can easily handle a large amount of data and high traffic workloads. It can distribute data across multiple nodes in a cluster for improved performance and fault tolerance. On the other hand, while Spanner is also designed for scalability, it provides automatic scaling within predefined limits and offers global consistency, which comes with additional coordination overhead.

3. Consistency Model: Cassandra follows a tunable consistency model, which allows choosing the level of consistency between replicas based on performance and reliability requirements. It provides eventual consistency by default but can be configured for strong consistency if needed. In contrast, Spanner offers strong consistency globally, ensuring that all replicas see the same consistent data at all times.

4. Query Language: Cassandra uses Cassandra Query Language (CQL), which is similar to SQL but has some differences due to its NoSQL nature. It supports querying using CQL statements and has built-in support for secondary indexes. On the other hand, Spanner supports SQL-like queries with its own enhancements for distributed querying and scale. It provides transactional SQL semantics and supports powerful features like joins, indexing, and multi-version concurrency control.

5. Architecture: Cassandra follows a masterless distributed architecture, where all nodes in the cluster are equal peers. It uses a peer-to-peer gossip protocol for coordination and event dissemination. Spanner, on the other hand, has a distributed architecture with a single-node leader and multiple followers. It uses the Paxos algorithm for consensus and replication to ensure consistency and fault tolerance.

6. Pricing Model: Cassandra is an open-source project and can be used without any licensing fees. However, the cost of running and managing a Cassandra cluster can vary based on factors like infrastructure costs, maintenance efforts, and support requirements. Google Cloud Spanner, being a managed service, has a usage-based pricing model that considers factors like the number of nodes, storage, and data transfer. It provides automatic replication and maintenance, reducing the operational overhead for users.

In summary, Cassandra is a highly scalable, schema-less NoSQL database with tunable consistency and a flexible data model. Google Cloud Spanner is a globally distributed relational database with strong consistency, automatic scaling, and transactional SQL semantics. The choice between the two depends on the specific requirements of the application, such as data model flexibility, consistency needs, scalability, query language preference, and cost considerations.