Polling vs Long Polling: Understanding the Basics

When building web applications that rely on real-time data or event-driven updates, choosing the right data-fetching strategy is crucial. Two widely known techniques are Polling and Long Polling. This article breaks down their definitions, pros and cons, and use cases.

What is Polling?

Polling is a technique where the client repeatedly sends requests to the server at regular intervals (e.g., every 5 seconds) to check for updates.

How it works:

• Client sends HTTP requests at intervals.
• The server responds immediately with the latest data (even if unchanged).

Note: This can lead to significant bandwidth wastage, especially when updates are infrequent, as data is repeatedly sent even if nothing has changed.

What is Long Polling?

Long polling is a more efficient variation where the client sends a request, and the server holds it open until new data is available to send or a timeout occurs.

How it works:

• The client sends a request.
• The server delays the response until new data is available.
• After receiving the response, the client immediately sends a new request.
• Or times out after a set number of seconds if no new data is present.

Use Cases

Polling:

• Stock price updates
• Notification checks in low-frequency environments
• Simple dashboards

Long Polling:

• Chat applications
• Live notifications (e.g., social media alerts)
• Real-time data feeds where WebSockets are unavailable

Notable Usage by Companies

• Google — Long Polling — Gmail and Google Chat in the early 2000s
• Facebook — Long Polling — Initial Facebook Chat implementation
• Twitter — Polling (early) — Early feed updates before moving to streaming
• Slack — Long Polling — Used before migrating to WebSockets
• Trello — Polling — Regular board updates in earlier versions
• GitHub — Polling — Used in APIs for checking CI status, notifications

Cloud Cost Estimation Example

Let’s consider a basic scenario to highlight how polling affects cloud bandwidth costs:

• Scenario: 1,000 users polling every 5 seconds
• Data per response: 1 KB
• Polling requests per minute: 12 per user × 1,000 users = 12,000 requests
• Data transferred per minute: 12,000 KB = 12 MB
• Per day: 12 MB × 60 minutes × 24 hours = ~17 GB/day
• Monthly usage: ~510 GB/month

Most cloud providers (e.g., AWS, GCP, Azure) charge for data transfer. At $0.09/GB (AWS average), bandwidth cost = $45.90/month

Note: Inbound traffic or bandwidth is free. Outbound is charged.

By contrast, long polling or WebSockets can drastically reduce this cost by only transferring data when it changes.

Conclusion

Polling and Long Polling both offer ways to fetch server updates when real-time communication is needed. Polling is simpler but less efficient, with higher bandwidth usage that can increase costs in cloud-hosted environments. Long Polling provides smarter updates with slightly more complexity. Choosing the right technique depends on your application’s needs, server capacity, and user experience expectations.