When building real-time applications, developers usually consider three approaches:
- Polling
- Server-Sent Events (SSE)
- WebSockets
At first, they may seem similar.
But choosing the wrong one can lead to performance issues, complexity, or scalability problems.
Let’s break them down clearly.
🔁 1. Polling — The Simplest Approach
Polling means the client repeatedly asks the server for updates.
Example:
Client → “Any update?”
Server → “No”
Client → “Any update?”
Server → “No”
Client → “Any update?”
Server → “Yes”
✅ Pros
- Very easy to implement
- Works everywhere
❌ Cons
- Wastes bandwidth (many useless requests)
- High server load
- Delayed updates
⚡ 2. Server-Sent Events (SSE)
With SSE, the client opens a single connection and waits for updates.
Client → open connection
Server → send updates when ready
Server → send updates when ready
SSE uses standard HTTP and the browser API: EventSource
✅ Pros
- Efficient (no repeated requests)
- Simple to implement
- Built-in reconnection
- Works over HTTP
❌ Cons
- One-way communication (server → client only)
- Not suitable for interactive apps (like chat)
🔄 3. WebSockets — Full Duplex Communication
WebSockets allow continuous two-way communication.
Client ⇄ Server ⇄ Client
They use a special protocol: WebSocket
✅ Pros
- Real-time two-way communication
- Low latency
- Great for interactive apps
❌ Cons
- More complex to implement
- Requires connection upgrade
- Harder to scale and debug
🧠 Key Differences
| Feature | Polling | SSE | WebSockets |
|---|---|---|---|
| Connection | Many requests | One long connection | Persistent upgraded connection |
| Direction | Request/response | Server → Client | Two-way |
| Efficiency | Low | High | Very High |
| Complexity | Low | Low | Medium/High |
🎯 When Should You Use Each?
Use Polling when:
- You need something quick and simple
- Real-time is not critical
Use SSE when:
- Updates are mostly server → client
- You want a simple real-time solution
- You need built-in reconnection
Examples:
- Notifications
- Live dashboards
- Stock updates
- Activity feeds
Use WebSockets when:
- You need two-way communication
Examples:
- Chat applications
- Multiplayer games
- Collaborative editing tools
⚠️ Common Mistake
A very common mistake is:
Using WebSockets for everything.
In many cases, SSE is:
- simpler
- easier to debug
- easier to scale
🧠 Interview Insight
If an interviewer asks:
“When would you choose SSE over WebSockets?”
A strong answer is:
When communication is mostly server-to-client and I want a simpler, HTTP-based streaming solution with built-in reconnection.
🚀 What’s Next
Now that you understand when to use SSE, let’s get practical.
In the next article, we’ll build a real SSE server using Python with FastAPI.
You’ll go from concept → working implementation.
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