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DEPRECATED: It's no longer possible to gain superuser access so this won't work on Supabase databases.

PostgreSQL Logical Replication with Supabase

How to set up a read-only replica using PostgreSQL Logical Replication with Supabase

Step 1: Set up a new project in Supabase to host your replica database

https://supabase.com

Step 2: Migrate the database schema to the new (replica) project

  1. Run ALTER ROLE postgres SUPERUSER in the old project's SQL editor
  2. Run pg_dump --clean --if-exists --schema-only --quote-all-identifiers -h [OLD_DB_HOST] -U postgres > schema_dump.sql from your terminal
  3. Run ALTER ROLE postgres NOSUPERUSER in the old project's SQL editor
  4. Run ALTER ROLE postgres SUPERUSER in the new project's SQL editor
  5. Run psql -h [NEW_DB_HOST] -U postgres -f schema_dump.sql from your terminal
  6. Run ALTER ROLE postgres NOSUPERUSER in the new project's SQL editor

Notes for this step

  • You must use the Supabase Dashboard SQL Editor to change the postgres user from NOSUPERUSER to SUPERUSER and vice-versa. The dashboard runs with the proper privileges to do this. Connecting to the database with any other tool using the postgres user will not work.
  • To find [OLD_DB_HOST] and [NEW_DB_HOST], go to your Supabase Settings Page and look under Connection Info / Host. It will have the format of db.zzzzzzzzzzzzzzzzzzzz.supabase.co where zzzzzzzzzzzzzzzzzzzz is your project reference number.
  • It's important to use the --schema-only option here, as you only want to dump the schema, and not the data.

Step 3: Create a publication on the production database

CREATE PUBLICATION my_publication FOR ALL TABLES;

Notes for this step

  • If you only want to replicate specific tables, you can use: CREATE PUBLICATION my_publication FOR TABLE table1, table2, table3;
  • The schema for each table in in your publication must exist in the replica database before you move on to create the subscription.
  • supabase_realtime is a reserved publication name, and cannot be used.

Step 4: Create a subscription on the replica database

CREATE SUBSCRIPTION my_subscription
CONNECTION 'postgresql://postgres:[PASSWORD]@[OLD_DB_HOST]:5432/postgres' 
PUBLICATION my_publication;

Notes for this section

  • [PASSWORD] is your postgres password, i.e. the password you created when you set up your project. (You can also reset your password from the Supabase Dashboard under Dashboard / Settings / Database / Reset Database Password)
  • [OLD_DB_HOST] is your primary database host name, used in the steps above
  • be sure to use port 5432 to connect to your PostgreSQL server, and not 6543, which is the pg_bouncer connection pooling port.

Debugging your replication

See Debugging PostgreSQL Logical Replication

Notes regarding database migrations / schema changes

  • Be careful with schema changes, they don't propagate to the replicas automatically, and will cause the replica to stop syncing.

  • If you use DROP CASCADE on the public schema when attempting to resync schemas, it can cause the realtime.subscription to drop.

Acknowlegements

Thanks to Colin from Zverse for pointing out some of these great debugging techniques that help solve issues related to database migrations.