Streaming Database Changes to Clients
Push live database updates to connected clients by listening to change events and relaying them over WebSockets in real time.
Streaming Database Changes to Clients is a free WebSockets & Realtime Systems Programming lesson on CoddyKit — lesson 3 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the WebSockets & Realtime Systems Programming learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
From Polling to Pushing
Instead of clients repeatedly asking the database for new data, you can push changes the moment they happen. The backend listens to the database and relays updates over WebSockets.
Change Data Capture
Change Data Capture (CDC) is the pattern of observing inserts, updates, and deletes as a stream of events instead of querying for differences.
Database Notification Mechanisms
Many databases emit change events:
- PostgreSQL:
LISTEN/NOTIFYor logical replication - MongoDB: change streams
- Firebase/Supabase: built-in realtime
Postgres LISTEN/NOTIFY
Postgres can send a notification on a channel that your backend subscribes to.
await client.query('LISTEN row_changed');Triggering Notifications
A trigger fires pg_notify on data changes, carrying a payload describing the change.
CREATE TRIGGER notify_change
AFTER INSERT ON orders
FOR EACH ROW EXECUTE FUNCTION notify_row();Receiving the Event
Your Node backend handles the notification and forwards it to interested WebSocket clients.
client.on('notification', (msg) => {
broadcast(JSON.parse(msg.payload));
});Filtering Who Gets Updates
Not every client cares about every change. Route updates by topic, user, or room so clients only receive relevant data.
function broadcast(change) {
toRoom('orders:' + change.userId, change);
}Sending Deltas, Not Snapshots
Transmit just what changed (a delta) rather than the whole dataset. Clients apply the delta to their local copy, saving bandwidth.
ws.send(JSON.stringify({ op: 'update', id: 42, fields: { status: 'shipped' } }));Initial State plus Stream
A common pattern: on connect, send a full snapshot, then stream incremental changes. The client stays in sync without re-fetching everything.
Handling Reconnects
After a reconnect a client may have missed changes. Send a fresh snapshot or a cursor of changes since its last known version to resync safely.
Best Practices
Stream changes reliably:
- Use CDC or LISTEN/NOTIFY instead of polling
- Filter updates per client
- Send deltas, not full snapshots
- Resync on reconnect to fill gaps
Quick Check
Test your change-streaming knowledge.
Recap
You streamed live database changes to clients:
- Use CDC / LISTEN-NOTIFY instead of polling
- Relay change events over WebSockets
- Filter per client and send deltas
- Snapshot on connect, resync on reconnect
Your data now stays live end to end.
Frequently asked questions
Is the “Streaming Database Changes to Clients” lesson free?
Yes — the full text of “Streaming Database Changes to Clients” is free to read here on the web, and the WebSockets & Realtime Systems Programming course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the WebSockets & Realtime Systems Programming course, upgrade to CoddyKit PRO.
What will I learn in “Streaming Database Changes to Clients”?
Push live database updates to connected clients by listening to change events and relaying them over WebSockets in real time. You practise WebSockets & Realtime Systems Programming with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start WebSockets & Realtime Systems Programming?
No prior experience is required. WebSockets & Realtime Systems Programming on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “Streaming Database Changes to Clients” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this WebSockets & Realtime Systems Programming lesson?
Yes. Every WebSockets & Realtime Systems Programming lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- WebSockets with RESTful APIs
- Bridging to Message Queues
- Streaming Database Changes to Clients