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Self-managed PostgreSQL

WAL level​

Run the following SQL command to change the WAL level from replica to logical and restart your database:

ALTER SYSTEM SET wal_level = logical;

If you have issues in other PostgreSQL hosting environments, please contact us, and we will send you detailed instructions on how to set it up.

Connection​

You can specify the same regular database credentials you use to connect to PostgreSQL from your code. And that's it, everything should just work!

Read-only credentials​

Alternatively, you can manually create read-only PostgreSQL database credentials to connect to the primary instance's WAL. At a high level, you need to run these commands that are safe to execute without any downtime or performance issues:

  • CREATE ROLE creates a new read-only user for Bemi to read database changes.
  • CREATE PUBLICATION creates a "channel" that we'll subscribe to and track changes in real-time.
  • REPLICA IDENTITY FULL enhances records stored in WAL to record the previous state (“before”) in addition to the tracked by default new state (“after”).
-- Create read-only user with REPLICATION permission
CREATE ROLE [username] WITH LOGIN NOSUPERUSER NOCREATEDB NOCREATEROLE REPLICATION PASSWORD '[password]';
-- Grant SELECT access to tables for selective tracking
GRANT SELECT ON ALL TABLES IN SCHEMA public TO [username];
-- Grant SELECT access to new tables created in the future for selective tracking
ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO [username];

-- Create "bemi" PUBLICATION to enable logical replication
CREATE PUBLICATION bemi FOR ALL TABLES;

-- Create a procedure to set REPLICA IDENTITY FULL for tables to track the "before" state on DB row changes
CREATE OR REPLACE PROCEDURE _bemi_set_replica_identity() AS $$ DECLARE current_tablename TEXT;
BEGIN
  FOR current_tablename IN SELECT tablename FROM pg_tables LEFT JOIN pg_class ON relname = tablename WHERE schemaname = 'public' AND relreplident != 'f' LOOP
    EXECUTE format('ALTER TABLE %I REPLICA IDENTITY FULL', current_tablename);
  END LOOP;
END $$ LANGUAGE plpgsql;
-- Call the created procedure
CALL _bemi_set_replica_identity();
-- Create a trigger function that calls the created procedure
CREATE OR REPLACE FUNCTION _bemi_set_replica_identity_func() RETURNS event_trigger AS $$
BEGIN CALL _bemi_set_replica_identity(); END $$ LANGUAGE plpgsql;
-- Create a trigger to set REPLICA IDENTITY FULL for all new created tables
CREATE EVENT TRIGGER _bemi_set_replica_identity_trigger ON ddl_command_end WHEN TAG IN ('CREATE TABLE')
EXECUTE FUNCTION _bemi_set_replica_identity_func();

Read-only credentials with manually managed permissions for each table​

Run the following queries if you want to isolate read access only to logical replication for certain tables and manage permissions manually instead of relying on our robust built-in selective tracking manageable through our UI.

-- Create read-only user with REPLICATION permission
CREATE ROLE [username] WITH LOGIN NOSUPERUSER NOCREATEDB NOCREATEROLE REPLICATION PASSWORD '[password]';

-- Create "bemi" PUBLICATION to enable logical replication for selected tables
CREATE PUBLICATION bemi FOR TABLE [table1], [table2];

-- Set REPLICA IDENTITY FULL for tables to track the "before" state on DB row changes
ALTER TABLE [table1] REPLICA IDENTITY FULL;
ALTER TABLE [table2] REPLICA IDENTITY FULL;

To enable data change tracking for a new table:

ALTER PUBLICATION bemi ADD TABLE [table3];
ALTER TABLE [table3] REPLICA IDENTITY FULL;

To stop data change tracking for a table:

ALTER PUBLICATION bemi DROP TABLE [table3];
ALTER TABLE [table3] REPLICA IDENTITY DEFAULT;