Long Polling

You just learned that regular polling wastes a massive amount of resources. The client asks "anything new?" every few seconds, and the server almost always responds "nope." Rinse and repeat, thousands of times, with nothing to show for it.

So someone had a clever idea: what if the server didn't respond immediately when there's nothing new? What if it just held the connection open and waited until something actually happened?

That's long polling. And it was the backbone of real-time web applications for over a decade. Facebook's original chat system? Long polling. Gmail's inbox notifications before they switched to other methods? Long polling. Slack's early versions? Long polling.

It's the trick that made the web feel "live" before WebSockets existed.

Long polling flips the script on regular polling:

1. The client sends an HTTP request to the server: "Any new data?"
2. If the server has new data, it responds immediately, just like regular polling
3. If the server has no new data, it holds the request open and waits
4. The server only responds when: (a) new data arrives, or (b) a timeout expires (typically 30-60 seconds)
5. The moment the client receives a response, it immediately sends another request
6. Go back to step 1

The server is saying: "I'll get back to you when I actually have something to tell you."

This eliminates nearly all the wasted requests. Instead of 12 empty responses per minute (polling every 5 seconds), you get maybe 1-2 responses, only when something actually happens.

The implementation detail most tutorials skip: how does the server know when new data arrives while holding a request? Three common approaches:

• Postgres LISTEN/NOTIFY: the database triggers a notification channel when a row is inserted. Your server subscribes to that channel.
• In-memory event emitter: a Node.js EventEmitter or Go channel that fires when the application writes new data.
• Short micro-poll: the server checks every 200ms internally, much cheaper than the client polling over HTTP because there's no network round trip.