Long Polling
The client sends a request and the server holds it open until new data is available or a timeout is reached. A workaround for real-time updates before WebSockets existed.
What is Long Polling?
The client sends a request and the server holds it open until new data is available or a timeout is reached. A workaround for real-time updates before WebSockets existed.
Long Polling is a intermediate-level concept that sits in the API Design & Protocols area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "Long Polling" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
Learn Long Polling in depth
Full interactive lesson with diagrams, code examples, real-world references, and a quiz.
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Lessons that touch on Long Polling as part of a larger topic.
See also
Related glossary terms you might want to look up next.
WebSocket
A protocol for full-duplex communication over a single TCP connection. Unlike HTTP, the server can push data to the client without being asked.
SSE
Server-Sent Events: a one-way channel where the server pushes updates to the client over HTTP. Simpler than WebSockets when you only need server-to-client streaming.
HTTP
The protocol powering the web. A request-response model where clients ask for resources and servers respond. Stateless by design.