Citus Blog

There is some good news for those of you wanting to shard your Postgres database in the cloud, so that as your data grows you have an easy way to scale out your Postgres database. I’m delighted to announce that Citus 10—the latest open source release of the Citus extension to Postgres—is now generally available in Hyperscale (Citus).

Hyperscale (Citus) is a built-in option in the Azure Database for PostgreSQL managed service, which has been around for a couple of years to help those of you who would rather focus on your application—and not on spending cycles managing your database.

It’s been an eventful time for Hyperscale (Citus) lately. If you’re interested in Postgres, distributed databases, and how to handle ever growing needs for your Postgres application or simply use Hyperscale (Citus), keep reading.

Citus is an open source extension to Postgres that enables horizontal scaling of your Postgres database. Citus distributes your Postgres tables, writes, and SQL queries across multiple nodes—parallelizing your workload and enabling you to use the memory, compute, and disk of a multi-node cluster. And Citus is available on Azure: Hyperscale (Citus) is a deployment option in Azure Database for PostgreSQL.

What’s really exciting to me is that we’ve made it easier and cheaper than ever to try and use Hyperscale (Citus). With Basic tier, you can now use Hyperscale (Citus) on a single node, parallelizing your operations and adopting a distributed database model from the very beginning. And you can now try Citus open source with a single docker run command—boom!

If you’ve worked with Ruby on Rails you likely have some understanding of how your database works with Rails, traditionally that has always meant specifying a single database per environment in your config/database.yml, possibly together with an environment setting like DATABASE_URL. Based on that configuration all reads and writes will access the database.

With Rails 6 this is about to change, thanks to the work of Eileen M. Uchitelle together with contributors from GitHub, Basecamp and Shopify. In the upcoming Rails 6 (currently in RC1), you will be able to easily change which database server you are connecting to, to support a variety of scenarios such as using read replicas and splitting your database into dedicated components.

The most interesting part, which we wanted to detail in this post, is related to configuring automatic queries against a read replicas, or follower database.

Citus extends Postgres to be a horizontally scalable database. By horizontally scalable, we mean the data is spread across multiple machines, and you're able to scale not only storage but also memory and compute—thus providing better performance. Without using something like Citus to transform PostgreSQL into a distributed database, sure you can add read replicas to scale, but you're still maintaining a single copy of your data. When you run into scaling issues with your Postgres database, adding a read replica and offloading some of your traffic to your read replica is a common bandaid to slow down the bleeding, but it is only a matter of time until even that doesn't work any further. Whereas with Citus, scaling out your database is as simple as dragging a slider and rebalancing your data.

Are read replicas still useful with horizontally scalable databases?

But that leaves a question, are read-replicas still useful? Well, sure they are.