Long Polling vs WebSockets vs Server-Sent Events

Let's talk about three different ways to get real-time updates in web applications, because choosing the right approach can make a huge difference in your app's performance.

Repeatedly asking the server for updates (Regular Polling isn't great because it wastes resources. Imagine refreshing the app every few seconds for a message that might never come. Your battery drains, and the server gets overwhelmed with unnecessary requests.

When your web app needs to receive live updates from a server, you have three main options: Long Polling, WebSockets, and Server-Sent Events (SSE).

Long Polling is smarter than Regular Polling. Instead of constantly checking, the client makes a request and the server holds onto it until there's actually new data to send. Once the server responds, the client immediately makes another request. While this is better than regular polling, it still has drawbacks because you need to create new connections frequently, which involves sending extra headers and using server resources.

WebSockets are more sophisticated. They create a persistent, two-way connection between the client and server. This means both sides can send data to each other at any time without establishing new connections. WebSockets are great for applications that need frequent, real-time updates like chat apps or live gaming. However, keeping these connections open can waste resources if you're not sending data frequently.

Server-Sent Events (SSE) offer a middle ground. Like WebSockets, they maintain a persistent connection, but they only allow the server to send data to the client (one-way communication). If the client needs to send data back, it uses regular HTTP requests. SSE also offers automatic reconnection if the connection drops. However, this can cause problems in large applications through something called the "Thundering Herd" problem - if the server goes down and comes back up, all clients trying to reconnect simultaneously might overwhelm it.

Here's a comparison of the three approaches: