Citus Blog

In my day to day, I get to work with many customers migrating their data to Postgres. I work with customers migrating from homogenous sources (PostgreSQL) and also from heterogenous database sources such as Oracle and Redshift. Why do people pick Postgres? Because of the richness of PostgreSQL—and features like stored procedures, JSONB, PostGIS for geospatial workloads, and the many useful Postgres extensions, including my personal favorite: Citus.

A large chunk of the migrations that I help people with are homogenous Postgres-to-Postgres data migrations to the cloud. As Azure Database for PostgreSQL runs open source Postgres, in many cases the application migration can be drop-in and doesn’t require a ton effort. The majority of the effort usually goes into deciding on and implementing the right strategy for performing the data migration.

When those of us who work on Postgres High Availability explain how HA in Postgres works, we often focus on the server side of the stack. Having a Postgres service running with the expected data set is all-important and required for HA, of course. That said, the server side of the stack is not the only thing that matters when implementing high availability. Application code has a super important role to play, too.

In this post, you will learn what happens to your application code and connections when a Postgres failover is orchestrated. Your application might be running on Postgres on-prem with HA configured—or in the cloud—or on a managed PostgreSQL service such as Azure Database for PostgreSQL. Now, if you’re running your app on top of a managed service with HA, you probably don’t need to worry about how to implement HA, as HA is managed by the service. But it’s still useful to understand what happens to your application when a Postgres failover occurs.

Once you start using the Citus extension to distribute your Postgres database, you may never want to go back. But what if you just want to experiment with Citus and want to have the comfort of knowing you can go back? Well, as of Citus 9.5, now there is a new undistribute_table() function to make it easy for you to, well, to revert a distributed table back to being a regular Postgres table.

If you are familiar with Citus, you know that Citus is an open source extension to Postgres that distributes your data (and queries) to multiple machines in a cluster—thereby parallelizing your workload and scaling your Postgres database horizontally. When you start using Citus—whether you’re using Citus open source or whether you’re using Citus as part of a managed service in the cloud—usually the first thing you need to do is distribute your Postgres tables across the cluster.