---
title: "Discussion on \"Realtime Systems: Polling, WebSockets, SSE, and Pub/Sub\" | Hashnode"
description: "Discussion on \"Realtime Systems: Polling, WebSockets, SSE, and Pub/Sub\". The question that started it all\nHow does WhatsApp deliver a message instantly?\nYou send a message, and it appears on your friend's phone within a fraction of a second — no refresh button, no waiting."
url: "https://hashnode.com/posts/realtime-systems-polling-websockets-sse-and-pub-sub/6a4d2c4903564e0cb1def54c"
---

[Feed](https://hashnode.com/feed) /

Discussion

# [Realtime Systems: Polling, WebSockets, SSE, and Pub/Sub](https://html-dev09.hashnode.dev/realtime-systems-polling-websockets-sse-and-pub-sub?utm_source=hashnode&utm_medium=feed)

The question that started it all How does WhatsApp deliver a message instantly? You send a message, and it appears on your friend's phone within a fraction of a second — no refresh button, no waiting.

Jul 7 · 17 min read · html-dev09.hashnode.dev  
Updated Aug 3  
Read the article

-   [#realtime](https://hashnode.com/tag/realtime)
-   [#web](https://hashnode.com/tag/web)
-   [#web-development](https://hashnode.com/tag/web-development)
-   [#development](https://hashnode.com/tag/development)
-   [#full-stack](https://hashnode.com/tag/full-stack)
-   [#chai](https://hashnode.com/tag/chai)
-   [#chaiaurcode](https://hashnode.com/tag/chaiaurcode)
-   [#websockets](https://hashnode.com/tag/websockets)
-   [#pubsub](https://hashnode.com/tag/pubsub)
-   [#sse](https://hashnode.com/tag/sse)
-   [#websocket](https://hashnode.com/tag/websocket)
-   [#polling](https://hashnode.com/tag/polling)
-   [#webdev](https://hashnode.com/tag/webdev)
-   [#dev](https://hashnode.com/tag/dev)
-   [#devlopment](https://hashnode.com/tag/devlopment)
-   [#chaicode](https://hashnode.com/tag/chaicode)
-   [#blogging](https://hashnode.com/tag/blogging)
-   [#blog](https://hashnode.com/tag/blog)
-   [#devops](https://hashnode.com/tag/devops)
-   [#reactjs](https://hashnode.com/tag/reactjs)
-   [#chaicode-webdev-cohort-2026](https://hashnode.com/tag/chaicode-webdev-cohort-2026)
-   [#cohort2026](https://hashnode.com/tag/cohort2026)

## Written by

[Kanishka Shashi](https://hashnode.com/@Kshashi22)

@Kshashi22 · Greater Noida, Gautam Buddha Nagar, Uttar Pradesh, IND

  
[View profile](https://hashnode.com/@Kshashi22)

Kshashi22

Hi, I'm Kanishka Shashi. I'm a Computer Science (AI & ML) student passionate about building, analyzing, and explaining technology. This blog is where I simplify complex concepts into practical, beginner-friendly guides. You'll find articles on Web Development, System Design, AI & LLMs, Data Analytics, SQL, Git/GitHub, and software engineering best practices. I enjoy exploring how modern technologies work under the hood and sharing insights through real-world examples and hands-on projects. Whether you're a student, developer, or tech enthusiast, I hope these articles help you learn something new and build better software. Learning in public. Building consistently. Sharing everything I discover.

## Responses

Markdown supported · ⌘↵ to post

No responses yet.