Citus Blog

Today we’re happy to announce our new activerecord-multi-tenant Ruby library, which enables easy scale-out of applications that are built on top of Ruby on Rails and follow a multi-tenant data model.

This Ruby library has evolved from our experience working with customers, scaling out their multi-tenant apps, and patching some restrictions that ActiveRecord and Rails currently have when it comes to automatic query building. It is based on the excellent acts_as_tenant library, and extends it for the particular use-case of a distributed multi-tenant database like Citus.

We talk with a number of Postgres users each week that are looking to scale out their database. First, we would never recommend scaling out until you truly have to, it’s always easier to scale your database up rather than out. It’s often not until over 100 GB of data that you need to think about sharding.

When you want to scale out though, you want it to be simple. For scaling a multi-tenant database, there’s three common approaches:

Citus is commonly used to scale out event data pipelines on top of PostgreSQL. Its ability to transparently shard data and parallelise queries over many machines makes it possible to have real-time responsiveness even with terabytes of data. Users with very high data volumes often store pre-aggregated data to avoid the cost of processing raw data at run-time. With Citus 6.0 this type of workflow became even easier using a new feature that enables pre-aggregation inside the database in a massively parallel fashion using standard SQL. For large datasets, querying pre-computed aggregation tables can be orders of magnitude faster than querying the facts table on demand.

When we started PGConf Silicon Valley we started it with the goal of helping to grow the Postgres community like many of the other conferences out there with a focus on a large scale west coast event. In our first two years of running the conference...

It’s a common misconception that high volume read-write workloads in PostgreSQL inevitably causes database inefficiency. We’ve heard of cases where users encounter slowdowns doing only a few hundred writes per second and turn to systems like Dynamo...

PGConf Silicon Valley, November 14-16, is barely under a month away and it's shaping up to be another great conference this year. Last year we had over 300 attendees to make it one of the larger Postgres conferences around, and this year we're expecting...

Everybody counts, but not always quickly. This article is a close look into how PostgreSQL optimizes counting. If you know the tricks there are ways to count rows orders of magnitude faster than you do already.

The problem is actually underdescribed...

SQL is a very powerful language for analyzing and reporting against data. At the core of SQL is the idea of joins and how you combine various tables together. One such type of join: outer joins are useful when we need to retain rows, even if it has no match on the other side.

And while the most common type of join, inner join, against tables A and B would bring only the tuples that have a match for both A and B, outer joins give us the ability to bring together from say all of table A even if they don’t have a corresponding match in table B. For example, let's say you keep customers in one table and purchases in another table. When you want to see all purchases of customers, you may want to see all customers in the result even if they did not do any purchases yet. Then, you need an outer join. Within this post we’ll analyze a bit on what outer joins are, and then how we support them in a distributed fashion on Citus.

If you’re building a SaaS application, you probably already have the notion of tenancy built in your data model. Typically, most information relates to tenants / customers / accounts and your database tables capture this natural relation.

With smaller amounts of data (10s of GB), it’s easy to throw more hardware at the problem and scale up your database. As these tables grow however, you need to think about ways to scale your multi-tenant database across dozens or hundreds of machines.

After our blog post on sharding a multi-tenant app with Postgres, we received a number of questions on architectural patterns for multi-tenant databases and when to use which. At a high level, developers have three options:

In any as-a-service business, which bills monthly, a key metric you track is MRR or monthly recurring revenue. It's good practice to have this on a dashboard and check it on a monthly, weekly, or even daily basis. If you have a simple pricing model that has set monthly plans, say like Netflix this is pretty easy to calculate:

SELECT sum(user_subscriptions.price)
FROM user_subscriptions
WHERE users_subscriptions.ended_at IS null;

The above will give you the run rate as of this exact moment in time. It gets a little more complicated to do this in a single query that gives it to you over time.