WebSockets vs. Polling vs. Long Polling: How Web Sockets work | System Design Interview Basics
Written by Massa Medi
In today's constantly connected world, delivering seamless, real time experiences on the web is not a luxury it's a necessity. Whether you're chatting with friends, watching live stock prices fluctuate, or immersing yourself in an online game, the tech behind these live interactions is what keeps the magic flowing. Enter WebSocket a protocol that’s engineered for true, bi-directional, real time communication between browsers and web servers.
Understanding the Basics: How Web Communication Worked Before WebSocket
Let’s roll back to the basics. Traditionally, HTTP web requests have served as the backbone of how web applications fetched and sent data. Here’s how it works:
- The browser (client) opens a connection to the server and requests some data.
- The server processes the request, prepares the response, and sends it back to the client.
- When the exchange is over, the connection is closed.
This pattern works perfectly for sites where you’re just browsing static content. But what if you need live updates, like seeing your friend’s new message in a chat or monitoring a sport score as the action unfolds? This is where things get tricky.
Meet Polling: The Old School Way To Check For Updates
One workaround developers have used for years is called polling. Polling is a common approach in countless AJAX applications and works like this:
- Your browser sends a request to the server (“Any new data for me?”).
- The server checks. If there’s new data, it sends it. If not, it returns an empty response.
- The browser waits a bit maybe one second, five seconds, or even every few milliseconds and then repeats the process.
Imagine standing at a ticket counter and asking, “Are my tickets ready?” every 5 seconds. Not only does this create a lot of repetitive traffic, but most of the responses are empty and it results in a whole lot of unnecessary connection churn. Every single poll creates a new HTTP connection, and most of time those connections are wasted asking for data that’s not there yet.
HTTP Long Polling: Less Noisy, Still Not Perfect
A clever evolution of polling is HTTP long polling. It’s the method that let websites get closer to real time updates before the advent of WebSocket. Here’s the big idea:
- Your browser sends a request to the server just like normal polling but this time, the server purposely waits before responding, if it doesn’t have new data yet.
- When data becomes available, the server responds immediately with all the updates.
- As soon as the browser gets the response, it quickly sends a new long polling request to the server, and the process repeats.
This “hanging” request style is sometimes called the hanging GET. If you imagine the client saying, “I’ll wait here until you have something for me,” you’ll understand the approach.
Long polling is an improvement over basic polling, but it comes with trade offs. Each request requires a new connection after the previous one times out. While long polling helps the server “push” data out as soon as it becomes available, it’s resource intensive especially at scale.
The Connection Problem: HTTP's One and Done Nature
Here’s a critical aspect: each time the browser needs data, it makes a fresh request, the server responds, and then the connection closes. Repeat indefinitely. There’s no always open line between the client and the server, which introduces delays and inefficiency. Long polling improved things, but with constant new connections, overheads, and tricky reconnection timing, it’s never quite seamless.
Enter WebSocket: Real Time, Full Duplex Communication Finally!
That’s where WebSocket triumphs. WebSocket lets the browser and server establish a persistent, open connection so both can communicate in two directions simultaneously and in real time. Think of it like a dedicated phone line open day and night, allowing messages to be sent between both parties whenever either has something to share. Here’s what makes WebSocket game changing:
- Full duplex: Both the client and the server can send messages independently at the same time if necessary.
- Super low latency: No more polling delays. Updates appear on the client instantly as they happen on the server.
- Less overhead: No need to constantly open and close connections like in HTTP based methods.
The protocol itself rides over TCP, just as HTTP does, but lets messages flow in both directions without re establishing the connection every time.
How a WebSocket Connection is Established
- Handshake: The client requests a WebSocket connection a special process called the WebSocket handshake.
- Upgrade: If the server supports it, it replies using specific headers to “upgrade” the connection and confirm the switch from HTTP to WebSocket.
- Persistent Channel: The handshake is complete; now the same TCP connection transforms into a full featured WebSocket pipeline, open for ongoing, real time data transfer in both directions.
Behind the scenes, WebSocket “handlers” on the server keep connections open for all active clients. These handlers are typically lightweight and efficient, managing many users at once.
Where WebSockets Shine: Real World Applications
WebSockets have become the backbone of modern, real time web applications. Let’s look at some practical use cases:
- Stock Trading Platforms: On sites where stock prices update moment to moment, WebSockets let the back end server push live data to the user interface seamlessly users see every tick in real time, without manual refreshes or polling delays.
- Chat Applications: In platforms like WhatsApp or Facebook Messenger, a single WebSocket connection per user enables instant message exchange, publishing, and broadcasting to individuals or groups without ever needing to reconnect for each message.
- Online Gaming: Fast paced gaming depends on real time reactions and screen updates. WebSockets ensure the UI refreshes instantly, supporting immediate communication between players and game servers.
When Not to Use WebSockets
Of course, WebSockets aren’t the right fit for every use case. If you only need to fetch data once or access information that rarely changes such as loading archival records or running simple queries standard HTTP requests are still the way to go. Using WebSockets here would be unnecessary overkill.
Conclusion: The Right Tool for the Right Job
WebSocket is a revolutionary technology for enabling blazing fast, interactive, bi directional communication between browsers and servers. While polling and long polling techniques have served the web well, they come with performance trade offs that WebSocket elegantly overcomes. However, as with all technologies, it’s important to choose the method that fits your application’s needs best. Thanks to innovations like WebSocket, the modern web is more real time and more interactive than ever before.
