Citus vs Google Cloud Spanner: What are the differences?

Introduction

Citus and Google Cloud Spanner are both distributed database systems that provide scalability and high availability for applications. However, there are several key differences between Citus and Google Cloud Spanner that set them apart from each other.

1. Data Model:

   • Citus is an extension to PostgreSQL, which means it inherits the same relational data model. It allows users to distribute tables across multiple nodes and use SQL for querying and modeling data.
   • Google Cloud Spanner, on the other hand, is a globally distributed relational database service. It provides a schema-based data model, but unlike Citus, it uses a semi-relational data model where data is structured as tables but also has hierarchical data types for structured data.

2. Scalability:

   • Citus uses sharding to horizontally scale the database by distributing data across multiple nodes. It allows users to scale out their database by adding more nodes.
   • Google Cloud Spanner also supports horizontal scaling, but it uses a different approach called "TrueTime" that offers strong consistency across geographically distributed regions. It automatically splits and replicates data across multiple nodes to provide high scalability.

3. Consistency Model:

   • Citus provides strong consistency within each shard, but it does not automatically provide strong consistency across all shards. Users can choose to enforce strong consistency at the application level if required.
   • Google Cloud Spanner guarantees external consistency, which means it provides strong consistency across all replicas and regions. It uses distributed transactions and a globally synchronized clock to ensure consistency.

4. Query Language:

   • Citus extends PostgreSQL, so it supports the same SQL query language and allows users to leverage the rich ecosystem of PostgreSQL extensions and tools.
   • Google Cloud Spanner also supports SQL for querying data, but it has some limitations compared to Citus. For example, it does not support all PostgreSQL extensions, and some complex queries may need to be rewritten to work with Spanner.

5. Managed Service:

   • Citus can be run as a managed service on the Citus Cloud, which simplifies deployment and management of the database. It offers automated backups, scaling, and monitoring.
   • Google Cloud Spanner is a fully managed service provided by Google Cloud. It handles database administration tasks such as replication, backups, and scaling automatically, allowing users to focus on developing their applications.

6. Pricing Model:

   • Citus is an open-source software that can be self-hosted or run on Citus Cloud, which offers different pricing tiers based on the number of nodes and storage required.
   • Google Cloud Spanner has a pay-as-you-go pricing model, where users are charged based on the amount of storage, compute, and network resources they consume. It offers different pricing tiers for different levels of performance and availability.

In summary, Citus and Google Cloud Spanner differ in their underlying data models, scalability approaches, consistency models, query languages, managed service offerings, and pricing models.