WebSocket vs Long Polling vs SSE: Differences and Use Cases
Real-Time Communication Comparison
Short Polling
Client requests at fixed intervals (e.g., every 5s) ❌ High latency, many wasted requests, server load
Long Polling
Client sends request; server holds until new data is ready ✅ More real-time than short polling ❌ Connection must be re-established after each response
Server-Sent Events (SSE)
One-directional: server pushes to client over HTTP long connection ✅ Simple, auto-reconnect, HTTP-compatible ❌ One-way only; client cannot send over same connection
WebSocket
Bidirectional, full-duplex, persistent TCP connection ✅ Lowest latency, efficient for frequent two-way communication ❌ Requires special load balancer config (sticky session or pub/sub)
Decision Guide
| Use Case | Recommended |
|---|---|
| Chat, collaborative editing | WebSocket |
| Notifications, live feed | SSE |
| Simple infrequent polling | Long Polling |
| Real-time market data | WebSocket or SSE |
Interview bonus: WebSocket horizontal scaling uses Redis Pub/Sub across nodes (e.g., Socket.io Redis Adapter).
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