Citus Blog

Interview with the Postgres committers who have joined the Postgres team at Microsoft by Sudhakar Sannakkayala (Partner Director, Azure Data) and Ozgun Erdogan (Principal, Azure Data)—cross-posted from the Azure Database for PostgreSQL Blog.

In recent years, the data landscape has seen strong innovation as a result of the onset of open source technologies. At the forefront, PostgreSQL has shown that it’s the open source database built for every type of developer. By staying true to its principles of being standards-compliant, highly programmable, and extensible, PostgreSQL has solidified its position as the “most loved database” of developers across the board—ranging from scenarios for OLTP, analytics, and business intelligence to processing various formats of geometric data using the PostGIS extension.

Today, we’re excited to announce that we have donated 1% of Citus Data’s stock to the non-profit PostgreSQL organizations in the US and Europe. The United States PostgreSQL Association (PgUS) has received this stock grant. PgUS will work with PostgreSQL Europe to support the growth, education, and future innovation of Postgres both in the US and Europe.

To our knowledge, this is the first time a company has donated 1% of its equity to support the mission of an open source foundation.

To coincide with this donation, we’re also joining the Pledge 1% movement, alongside well-known technology organizations such as Atlassian, Twilio, Box, and more.

One of the primary challenges with scaling SaaS applications is the database. While you can easily scale your application by adding more servers, scaling your database is a way harder problem. This is particularly true if your application benefits from relational database features, such as transactions, table joins, and database constraints.

At Citus, we make scaling your database easy. Over the past year, we added support for distributed transactions, made Rails and Django integration seamless, and expanded on our SQL support. We also documented approaches to scaling your SaaS database to thousands of customers.

Today, we’re excited to announce the latest release of our distributed database—Citus 7.5. With this release, we’re adding key features that make scaling your SaaS / multi-tenant database easier. If you’re into bulleted lists, these features include the following.

Today, we’re excited to announce the latest release of our distributed database, Citus 7.4! Citus scales out PostgreSQL through sharding, replication, and query parallelization.

Ever since we open sourced Citus as a Postgres extension, we have been incorporating your feedback into our database. Over the past two years, our release cycles went down from six to four to two months. As a result, we have announced 10 new Citus releases, where each release came with notable new features.

Shorter release cycles and more features came at a cost however. In particular, we added new distributed planner and executor logic to support different use cases for multi-tenant applications and real-time analytics. However, we couldn’t find the time to refactor this new logic. We found ourselves accumulating technical debt. Further, our distributed SQL coverage expanded over the past two years. With each year, we ended spending more and more time on testing each new release.

In Citus 7.4, we focused on reducing technical debt related to these items. At Citus, we track our development velocity with each release. While we fix bugs in every release, we found that a full release focused on addressing technical debt would help to maintain our release velocity. Also, a cleaner codebase leads to a happier and more productive engineering team.

Today, we’re excited to announce Citus 7.3—the latest release of our distributed database that scales out Postgres. Citus 7.3 improves support for complex analytical queries, provides integration with Tableau and other BI tools, and integrates with the open source Postgres extension, TopN.

The features in this latest Citus database release are particularly important for real-time analytics workloads. In these workloads, users typically need to ingest data in real time and run analytical queries with sub-second response times. A good example is when you’re serving a dashboard to thousands of customers and your database needs to provide fast replies over billions of rows.

Here’s a quick overview of what’s new in Citus. For an overview of other recent Citus features, check out these blog entries about TopN for your Postgres database and Citus 7.2.

The Citus distributed database scales out PostgreSQL through sharding, replication, and query parallelization. For replication, our database as a service (by default) leverages the streaming replication logic built into Postgres.

When we talk to Citus users, we often hear questions about setting up Postgres high availability (HA) clusters and managing backups. How do you handle replication and machine failures? What challenges do you run into when setting up Postgres HA?

The PostgreSQL database follows a straightforward replication model. In this model, all writes go to a primary node. The primary node then locally applies those changes and propagates them to secondary nodes.

In the context of Postgres, the built-in replication (known as “streaming replication”) comes with several challenges:

• Postgres replication doesn’t come with built-in monitoring and failover. When the primary node fails, you need to promote a secondary to be the new primary. This promotion needs to happen in a way where clients write to only one primary node, and they don’t observe data inconsistencies.
• Many Postgres clients (written in different programming languages) talk to a single endpoint. When the primary node fails, these clients will keep retrying the same IP or DNS name. This makes failover visible to the application.
• Postgres replicates its entire state. When you need to construct a new secondary node, the secondary needs to replay the entire history of state change from the primary node. This process is resource intensive—and makes it expensive to kill nodes in the head and bring up new ones.

The first two challenges are well understood. Since the last challenge isn’t as widely recognized, we’ll examine it in this blog post.

Today, we’re excited to announce our latest release of our distributed database—Citus 7.2. With this release, we’re making Citus more of a drop-in replacement for your single-node Postgres database, so you don’t need to adapt your SQL for a distributed system.

For multi-tenant applications where the single-tenant queries were scoped to a single machine, Citus already provided full SQL support. . The improvements in Citus 7.2 take our support for distributed SQL one big step further. With Citus database version 7.2, we now extend our distributed SQL support to queries that run on data spread across a cluster of machines. This becomes particularly important for real-time analytics workloads, where even the most complex SELECT queries need to be parallelized across machines.

If you’re into bulleted lists, here’s the quick overview of what’s new in Citus database version 7.2 for distributed queries that span across machines. For an overview of other recent Citus features check out these blogs about distributed transactions and Citus 7.1.

So about two weeks ago we had a stealth release of Citus 7.1. And while we have already blogged a bit about the recent (and exciting) update to our fully-managed database as a service–Citus Cloud—and about our newly-added support for distributed transactions, it’s time to share all the things about our latest Citus 7.1 release.

If you’re into bulleted lists, here’s the quick overview of what’s in Citus 7.1:

• Distributed transaction support
• Zero-downtime shard rebalancer
• Window function enhancements
• Distinct ON/count(distinct) enhancements
• Additional SQL enhancements
• Checking for new software updates

Distributed transactions are one of the meanest, baddest problems in relational databases. With the release of Citus 7.1, distributed transactions are now available to all our users. In this article, we are going to describe how we built distributed transaction support into Citus by using PostgreSQL modules. But first, let’s give an overview of what a distributed transaction is.

(If this sounds familiar, that’s because we first announced distributed transactions as part of last week’s Citus Cloud 2 announcement. The Citus Cloud announcement centered on other new useful capabilities —such as our warp feature to streamline migrations from single-node Postgres deployments to Citus Cloud — but it seems worthwhile to dedicate an entire post to distributed transactions.)

“Thirty years ago, my older brother was trying to get a report on birds written that he’d had three months to write. It was due the next day.

We were out at our family cabin in Bolinas, and he was at the kitchen table close to tears, surrounded by binder paper and pencils and unopened books on birds, immobilized by the hugeness of the task ahead. Then my father sat down beside him, put his arm around my brother’s shoulder, and said, ‘Bird by bird, buddy. Just take it bird by bird.’”

— Bird by Bird: Some Instructions on Writing and Life, by Anne LaMott

When we started working on Citus, our vision was to combine the power of relational databases with the elastic scale of NoSQL. To do this, we took a different approach. Instead of building a new database from scratch, we leveraged PostgreSQL’s new extension APIs. This way, Citus would make Postgres a distributed database and integrate with the rich ecosystem of tools you already use.

When PostgreSQL is involved, executing on this vision isn’t a simple task. The PostgreSQL manual offers 3,558 pages of features built over two decades. The tools built around Postgres use and combine these features in unimaginable ways.

After our Citus open source announcement, we talked to many of you about scaling out your relational database. In every conversation, we’d hear about different Postgres features that needed to scale out of the box. We’d take notes from our meeting and add these features into an internal document. The list would keep getting longer, and longer, and longer.

Like the child writing a report on birds, the task ahead felt insurmountable. So how do you take a solid relational database and make sure that all those complex features scale? You take it bird by bird. We broke down the problem of scaling into five hundred smaller ones and started implementing these features one by one.