Database sharding on Heroku

Question

At some point in the next few months our app will be at the size where we need to shard our DB. We are using Heroku for hosting, Node.js/PostgreSQL stack.

Conceptually, it makes sense for our app to have each logical shard represent one user and all data associated with that user (each user of our app generates a lot of data, and there are no interactions between users). We need to retain the ability for the user to do complex ad-hoc querying on their data. I have read many articles such as this one which talk about sharding: http://www.craigkerstiens.com/2012/11/30/sharding-your-database/

Conceptually, I understand how Sharding works. However in practice I have no idea how to go about implementing this on Heroku, in terms of what code I need to write and what parts of my application I need to modify. A link to a tutorial or some pointers would be much appreciated.

Here are some resources I have already looked at:

Have you checked out Octopus? https://github.com/tchandy/octopus — catsby, Feb 13 '13 at 19:52

score 1 · Answer 1 · answered Apr 17 '17 at 14:05

As the author of the first article happy to chime in further. When it comes to sharding one of the very key components is what key are you sharding on. The complexity of sharding really comes into play when you have data that is intermingled across different physical nodes. If you're something like a multi-tenant app then modeling all your data around this idea of a tenant or customer can fit very cleanly in this setup. In that case you're going to want to break up all tables that are related to customer and shard them the same way as other tenant related tables.

As for doing this on Heroku, there are two options. You can roll your own with Heroku Postgres and application logic, or using something like Citus (which is an add-on that helps manage more of this for you.

For rolling your own, you'll first create the various application logic to handle creating all your shards and knowing where to route the appropriate queries to. For Rails there are some gems to help wtih this like activerecord-multi-tenant or apartment. When it comes to actually moving to sharding and that migration, what you'll want to do is create a Heroku follower to start. During the migration you'll have it start un-following. Then you'll remove half of the data from the original primary and the other half from the follower you separated accordingly.

Citus is no longer available as an add-on in Heroku. (Perhaps, this could be related to the acquisition of Citus by Microsoft Azure) — Yassine Belmamoun, Jan 19 '21 at 05:19

score 0 · Answer 2 · answered Apr 26 '13 at 14:22

I am not sure I would call this "sharding."

In LedgerSMB here is how we do things. Each company (business entity) is a separate database with fully separate data. Data cannot be shared between companies. One postgreSQL cluster can run any number of company databases. We have an administrative interface that creates the database and loads the schema. The administrative interface can also create new users, which can be shared between companies (optionally). I don't know quite how well it would work to share users between dbs on Heroku but I am including that detail in terms of how we work with PostgreSQL.

So this is a viable approach.

What you really need is something to spin up databases and manage users in an automated way. From there you can require that the user specifies a company name that you can map to a database however you'd like (this mapping could be stored in another database for example).

I know this is fairly high level. It should get you started however.

Database sharding on Heroku

2 Answers2