Glossary

Long Polling

Long polling is a technique for simulating push notifications over HTTP. The client sends a request; the server holds it open until new data appears (or a timeout occurs), then responds. The client immediately sends the next request. An older "real-time" approach before WebSocket.

Flow

Client                    Server
  |-- GET /poll --------->|
  |                       | (waiting for new data)
  |                       | (30 seconds...)
  |<-- 200 {data} --------|
  |-- GET /poll --------->| (new request immediately)
  |                       |

Benefits

Works everywhere — plain HTTP, no special protocols
Simpler to implement than WebSocket

Drawbacks

Many open connections burden the server
Latency = time between response and new request
HTTP overhead on every cycle

When still relevant

Environments where WebSocket and SSE are unavailable (corporate proxies, old browsers). In modern web apps, usually replaced by SSE or WebSocket.