WebSocket vs HTTP Long Polling

In the realm of real-time web applications, developers often face the choice between WebSocket and HTTP Long Polling. Both methods enable communication between the client and server, but they do so in fundamentally different ways. Understanding these differences is crucial for system design, especially when preparing for technical interviews at top tech companies.

What is HTTP Long Polling?

HTTP Long Polling is a technique that allows a client to request information from a server in a way that simulates a real-time connection. Here’s how it works:

1. The client sends an HTTP request to the server.
2. If the server has no new information, it holds the request open until new data is available or a timeout occurs.
3. Once the server has new data, it responds to the client, which then processes the data and immediately sends a new request.

Advantages of HTTP Long Polling:

• Simplicity: It uses standard HTTP requests, making it easy to implement with existing web technologies.
• Compatibility: Works well with existing infrastructure, including firewalls and proxies that may not support WebSocket.

Disadvantages of HTTP Long Polling:

• Latency: There is a delay between the server sending data and the client receiving it, as the client must wait for the server to respond.
• Overhead: Each request-response cycle incurs HTTP overhead, which can lead to increased bandwidth usage and server load.

What is WebSocket?

WebSocket is a protocol that provides full-duplex communication channels over a single TCP connection. It allows for persistent connections between the client and server, enabling real-time data exchange. Here’s how it works:

1. The client initiates a WebSocket connection by sending a handshake request to the server.
2. Once the connection is established, both the client and server can send messages to each other at any time without the need to re-establish the connection.

Advantages of WebSocket:

• Real-time Communication: WebSocket allows for instant data transfer, making it ideal for applications that require real-time updates, such as chat applications or live notifications.
• Reduced Overhead: After the initial handshake, data is sent in a lightweight format, reducing bandwidth usage compared to HTTP Long Polling.

Disadvantages of WebSocket:

• Complexity: Implementing WebSocket can be more complex than HTTP Long Polling, especially in terms of handling connection states and fallbacks.
• Compatibility Issues: Some older browsers and network configurations may not support WebSocket, which can limit its use in certain environments.

When to Use Each?

• Use HTTP Long Polling when:

  • You need a simple solution that works with existing HTTP infrastructure.
  • Your application does not require real-time updates and can tolerate some latency.

• Use WebSocket when:

  • Your application demands real-time communication with minimal latency.
  • You are building a highly interactive application, such as online gaming or collaborative tools.

Conclusion

Both WebSocket and HTTP Long Polling have their place in web application development. Understanding their differences, advantages, and disadvantages will help you make informed decisions when designing systems for real-time communication. As you prepare for technical interviews, be ready to discuss these concepts and their implications in system design.