Building a Real-Time Application with PGX and PostgreSQL LISTEN/NOTIFY in Go

Real-time applications have become increasingly important in modern software development. In this post, we’ll explore how to build a real-time application using Go, PGX, and PostgreSQL’s powerful LISTEN/NOTIFY feature. This combination allows us to create responsive applications that can react to database changes instantly.

Understanding PostgreSQL LISTEN/NOTIFY

PostgreSQL’s LISTEN/NOTIFY is a powerful pub/sub mechanism that enables real-time communication between database clients. Think of it as a built-in messaging system where database events can trigger notifications to connected applications.

Setting Up the Project

First, let’s set up our Go project with PGX. We’ll need to install the necessary dependencies:

go mod init realtime-app
go get github.com/jackc/pgx/v4

Implementing the Listener

Here’s how we can create a basic listener that connects to PostgreSQL and waits for notifications:

func createListener(connString string) (*pgx.Conn, error) {
    conn, err := pgx.Connect(context.Background(), connString)
    if err != nil {
        return nil, fmt.Errorf("unable to connect to database: %v", err)
    }

    _, err = conn.Exec(context.Background(), "LISTEN data_changes")
    if err != nil {
        return nil, fmt.Errorf("unable to start listening: %v", err)
    }

    return conn, nil
}

Creating the Notification Trigger

We need to create a PostgreSQL trigger that will send notifications when data changes:

CREATE OR REPLACE FUNCTION notify_data_changes()
RETURNS trigger AS $$
BEGIN
    PERFORM pg_notify('data_changes', row_to_json(NEW)::text);
    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

Handling Notifications in Real-Time

Here’s how we can process the notifications in our Go application:

func handleNotifications(conn *pgx.Conn) {
    for {
        notification, err := conn.WaitForNotification(context.Background())
        if err != nil {
            log.Printf("Error waiting for notification: %v", err)
            continue
        }

        // Process the notification
        fmt.Printf("Received notification: %s\n", notification.Payload)
    }
}

Best Practices and Considerations

1. Always handle connection losses gracefully
2. Implement reconnection logic
3. Use connection pooling for better performance
4. Consider payload size limitations
5. Implement error handling and logging

Remember that LISTEN/NOTIFY is not guaranteed delivery - if your application is offline, it will miss notifications. Consider implementing additional mechanisms like timestamp-based polling for critical data synchronization.

Conclusion

Using PGX with PostgreSQL’s LISTEN/NOTIFY feature provides a powerful foundation for building real-time applications in Go. This approach is particularly useful for scenarios requiring immediate updates, such as chat applications, real-time dashboards, or collaborative tools.