This is a guide on how to create a generic PostgreSQL peer which you can use for replication in PeerDB.

If you use one of the supported providers (in the sidebar), please refer to the specific guide for that provider.

1

Enabling Replication on the Postgres Instance

  1. To enable replication on your PostgreSQL instance, we need to make sure that the following settings are set:

    wal_level = logical

    To check the same, you can run the following SQL command:

    SHOW wal_level;

    The output should be logical. If not, run:

    ALTER SYSTEM SET wal_level = logical;

  2. Additionally, the following settings are recommended to be set on the PostgreSQL instance:

    max_wal_senders > 1
max_replication_slots >= 4

    To check the same, you can run the following SQL commands:

    SHOW max_wal_senders;
SHOW max_replication_slots;

    If the values do not match the recommended values, you can run the following SQL commands to set them:

    ALTER SYSTEM SET max_wal_senders = 10;
ALTER SYSTEM SET max_replication_slots = 10;

  3. If you have made any changes to the configuration as mentioned above, you NEED to RESTART the PostgreSQL instance for the changes to take effect.

2

Creating a user with permissions and publication

Let’s create a new user for PeerDB with the necessary permissions suitable for CDC, and also create a publication that we’ll use for replication.

The PeerDB user must not be restricted by RLS policies, as it can lead to missing data. You can disable RLS policies for the user by running the below command:

ALTER USER peerdb_user BYPASSRLS;

For this, you can connect to your PostgreSQL instance and run the following SQL commands:

  CREATE USER peerdb_user PASSWORD 'peerdb_password';
  GRANT USAGE ON SCHEMA "public" TO peerdb_user;
  GRANT SELECT ON ALL TABLES IN SCHEMA "public" TO peerdb_user;
  ALTER DEFAULT PRIVILEGES IN SCHEMA "public" GRANT SELECT ON TABLES TO peerdb_user;

-- Give replication permission to the USER
  ALTER USER peerdb_user REPLICATION;

-- Create a publication. We will use this when creating the mirror
  CREATE PUBLICATION peerdb_publication FOR ALL TABLES;

Make sure to replace peerdb_user and peerdb_password with your desired username and password.

Also, remember to use the same publication name when creating the mirror in PeerDB.

3

Enabling connections in pg_hba.conf to the PeerDB User

If you are self serving, you need to allow connections to the PeerDB user from the PeerDB IP addresses by following the below steps. If you are using a managed service, you can do the same by following the provider’s documentation.

  1. Make necessary changes to the pg_hba.conf file to allow connections to the PeerDB user from the PeerDB IP addresses. An example entry in the pg_hba.conf file would look like:

    host    all   peerdb_user     0.0.0.0/0          scram-sha-256

  2. Reload the PostgreSQL instance for the changes to take effect:

    SELECT pg_reload_conf();
4

Create the Peer on PeerDB

  1. Head over to PeerDB UI and click on Create Peer. Select Postgres as the source.

  2. Now you can fill in the connection details of the PostgreSQL instance, but make sure to use the username and password you created earlier in the SQL commands in Step 2.

Create the PostgreSQL Peer

  1. Click on Validate and once that’s green, you can go ahead and click on Create to create the peer!
5

Increase max_slot_wal_keep_size

This is a recommended configuration change to ensure that large transactions/commits do not cause the replication slot to be dropped.

You can increase the max_slot_wal_keep_size parameter for your PostgreSQL instance to a higher value (at least 100GB or 102400) by updating the postgresql.conf file.

max_slot_wal_keep_size = 102400

You can reload the PostgreSQL instance for the changes to take effect:

SELECT pg_reload_conf();

For better recommendation of this value you can contact the PeerDB team.

When creating the Mirror, make sure to reuse the same publication you created earlier in Step 2