Long Polling vs SSE vs WebSocket

HTTP Long Polling

Mechanism: Client sends a request, server holds it open until data is available or a timeout occurs, then responds and closes the connection. Client immediately sends another request, creating a continuous loop.

Pros

• Simple, works over standard HTTP without special libraries.
• Works behind most firewalls and proxies.

Cons

• Inefficient for high-frequency updates due to frequent polling and connection overhead.
• Server-side resource usage can be high due to many open connections.

Server-Sent Events (SSE)

Mechanism: Unidirectional communication from server to client over a single, long-lived HTTP connection. Server pushes events to the client as they occur.

Pros

• More efficient than Long Polling for one-way updates.
• Reduced server-side resource usage.
• Simpler JavaScript API for client-side handling.

Cons

• Still relies on HTTP, not as efficient as WebSockets for bidirectional communication.
• Limited browser support compared to WebSockets.

WebSockets

Mechanism: Full-duplex, bidirectional communication over a persistent TCP connection. Enables real-time, two-way data exchange between client and server.

Pros

• Most efficient for real-time, bidirectional communication.
• Low latency, low overhead.
• Wide browser support.
• Can handle binary data and messages of any size.

Cons

• Requires WebSocket-specific libraries and protocols.
• Might be blocked by some firewalls or proxies.