Realtime Server

Supabase Realtime is a Change Data Capture server. It allows you to listen to Postgres changes.

If you want to host your own Realtime server, you have options to host using Docker, AWS, DigitalOcean, or build from source.

What is this?

This is an Elixir server (Phoenix) that allows you to listen to changes in your database via websockets.

It works like this:

  1. the Phoenix server listens to PostgreSQL's replication functionality (using Postgres' logical decoding)
  2. it converts the byte stream into JSON
  3. it then broadcasts over websockets.

Cool, but why not just use Postgres' NOTIFY?

A few reasons:

  1. You don't have to set up triggers on every table
  2. NOTIFY has a payload limit of 8000 bytes and will fail for anything larger. The usual solution is to send an ID then fetch the record, but that's heavy on the database
  3. This server consumes one connection to the database, then you can connect many clients to this server. Easier on your database, and to scale up you just add realtime servers

What are the benefits?

  1. The beauty of listening to the replication functionality is that you can make changes to your database from anywhere - your API, directly in the DB, via a console etc - and you will still receive the changes via websockets.
  2. Decoupling. For example, if you want to send a new slack message every time someone makes a new purchase you might build that functionality directly into your API. This allows you to decouple your async functionality from your API.
  3. This is built with Phoenix, an extremely scalable Elixir framework

Quick start

We have set up some simple examples that show how to use this server:

Client libraries

Server

Database set up

There are a some requirements for your database

  1. It must be Postgres 10+ as it uses logical replication
  2. Set up your DB for replication
    1. it must have the wal_level set to logical. You can check this by running SHOW wal_level;. To set the wal_level, you can call ALTER SYSTEM SET wal_level = logical;
    2. You must set max_replication_slots to at least 1: ALTER SYSTEM SET max_replication_slots = 5;
  3. Create a PUBLICATION for this server to listen to: CREATE PUBLICATION supabase_realtime FOR ALL TABLES;
  4. [OPTIONAL] If you want to receive the old record (previous values) on UPDATE and DELETE, you can set the REPLICA IDENTITY to FULL like this: ALTER TABLE your_table REPLICA IDENTITY FULL;. This has to be set for each table unfortunately.

Server set up

The easiest way to get started is just to use our docker image. We will add more deployment methods soon.

# Update the environment variables to point to your own database
docker run \
-e DB_HOST='docker.for.mac.host.internal' \
-e DB_NAME='postgres' \
-e DB_USER='postgres' \
-e DB_PASSWORD='postgres' \
-e DB_PORT=5432 \
-e PORT=4000 \
-e HOSTNAME='localhost' \
-e SECRET_KEY_BASE='SOMETHING_SUPER_SECRET' \
-p 4000:4000 \
supabase/realtime

OPTIONS

DB_HOST # {string} Database host URL
DB_NAME # {string} Postgres database name
DB_USER # {string} Database user
DB_PASSWORD # {string} Database password
DB_PORT # {number} Database port
SLOT_NAME # {string} A unique name for Postgres to track where this server has "listened until". If the server dies, it can pick up from the last position. This should be lowercase.
PORT # {number} Port which you can connect your client/listeners

Contributing

  • Fork the repo on GitHub
  • Clone the project to your own machine
  • Commit changes to your own branch
  • Push your work back up to your fork
  • Submit a Pull request so that we can review your changes and merge

Releasing

  • Make a commit to bump the version in mix.exs
  • Tag the commit

To trigger a release you must tag the commit, then push to origin.

git tag -a 0.x.x -m "Some release details / link to release notes"
git push origin 0.x.x

License

This repo is licensed under Apache 2.0.