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Polling vs Long Polling vs WebSockets vs Webhooks - System Design
Table of Contents
- ?? 1. Core Idea (1-line difference)
- ?? 2. Polling (Basic)
- ? What it does
- ?? Key Insight
- ??? Architecture Signals (Use when)
- ? Problems
- ?? FAANG Q&A
- ?? Script
- ?? 3. Long-Polling (Improved Polling)
- ? What it does
- ?? Key Insight
- ??? Architecture Signals (Use when)
- ? Problems
- ?? FAANG Q&A
- ?? Script
- ?? 4. WebSockets (Best for Real-Time)
- ? What it does
- ?? Key Insight
- ??? Architecture Signals (Use when)
- ? Problems
- ?? FAANG Q&A
- ?? Script
- ?? 5. Webhooks (Server-to-Server Push)
- ? What it does
- ?? Key Insight
- ??? Architecture Signals (Use when)
- ? Problems
- ?? FAANG Q&A
- ?? Script
- ?? 6. Key Differences (Interview Table)
- ?? Script
- ?? 7. Real Architecture (FAANG Level)
- ? Combined Usage (VERY IMPORTANT)
- ?? Why?
- ?? FAANG Q&A
- ?? Script
- ?? 8. Strong Signals vs Weak Signals
- ?? Choose Polling
- ?? Choose Long-Polling
- ?? Choose WebSockets
- ?? Choose Webhooks
- ?? Weak Signals
- ?? 9. FAANG-Level Insights (Added)
- ?? 1. Backpressure Handling (WebSockets)
- ?? 2. Connection Scaling
- ?? 3. Retry Logic (Webhooks)
- ?? 4. Hybrid Systems
- ?? Final Ultra-Short Summary
?? 1. Core Idea (1-line difference)
- Polling ? Client keeps asking
- Long-Polling ? Client asks, server waits
- WebSockets ? Open continuous connection
- Webhooks ? Server pushes to another server
?? Script
�Polling asks repeatedly, long-polling waits for data, WebSockets keep a live connection, and webhooks push events server-to-server.�
?? 2. Polling (Basic)
? What it does
- Client sends request every X seconds
- Server responds immediately
?? Key Insight
?? Simple but inefficient
??? Architecture Signals (Use when)
- Low frequency updates
- Simple systems / prototypes
- No real-time requirement
? Problems
- High unnecessary requests ?
- Latency depends on interval
?? FAANG Q&A
Q: Why bad at scale? ?? Millions of useless requests.
Q: When acceptable? ?? Non-critical updates (e.g., refresh every 5 min).
?? Script
�Polling is simple but inefficient since clients repeatedly request data even when nothing changes.�
?? 3. Long-Polling (Improved Polling)
? What it does
- Client sends request
- Server holds connection until data arrives
- Then client reconnects
?? Key Insight
?? Near real-time using HTTP
??? Architecture Signals (Use when)
- Need near real-time
- Cannot use WebSockets
- HTTP-only environments
? Problems
- Server resource heavy (open connections)
- Still request-response cycle
?? FAANG Q&A
Q: Better than polling? ?? Yes, fewer empty responses.
Q: Limitation? ?? Not truly bidirectional.
?? Script
�Long-polling reduces unnecessary requests by holding the connection until data is available.�
?? 4. WebSockets (Best for Real-Time)
? What it does
- Persistent bi-directional connection
- Both client & server send data anytime
?? Key Insight
?? True real-time communication
??? Architecture Signals (Use when)
- Chat apps, gaming, trading apps
- High-frequency updates
- Low latency critical
? Problems
- Complex scaling
- Connection management required
?? FAANG Q&A
Q: Why fastest? ?? No repeated HTTP overhead.
Q: Challenge? ?? Managing millions of open connections.
?? Script
�WebSockets provide a persistent connection enabling real-time bidirectional communication with minimal latency.�
?? 5. Webhooks (Server-to-Server Push)
? What it does
- Server sends HTTP POST on event
- No polling required
?? Key Insight
?? Event-driven push (no client involvement)
??? Architecture Signals (Use when)
- External integrations (payments, GitHub)
- Event-driven systems
- Avoid polling APIs
? Problems
- One-way communication
- Requires reliable endpoint
?? FAANG Q&A
Q: Why better than polling APIs? ?? Only sends data when event happens.
Q: Risk? ?? Missed events if endpoint fails.
?? Script
�Webhooks allow servers to notify other systems instantly when events occur, eliminating the need for polling.�
?? 6. Key Differences (Interview Table)
| Method | Communication | Latency | Overhead | Use Case |
|---|---|---|---|---|
| Polling | Client ? Server | High | High | Simple apps |
| Long-Polling | Client ? Server (wait) | Medium-Low | Medium | Fallback real-time |
| WebSockets | Bi-directional | Low | Low | Real-time apps |
| Webhooks | Server ? Server | Low | Low | Integrations |
?? Script
�Polling is inefficient, long-polling improves it, WebSockets enable real-time communication, and webhooks handle event-driven integrations.�
?? 7. Real Architecture (FAANG Level)
? Combined Usage (VERY IMPORTANT)
External Service ? Webhook ? Backend
?
WebSocket Server
?
Clients
?? Why?
- Webhooks ? receive events
- WebSockets ? push to users
?? FAANG Q&A
Q: How to notify users of Stripe payment? ?? Webhook ? backend ? WebSocket ? client.
Q: Fallback if WebSockets fail? ?? Long-polling.
?? Script
�In production, I use webhooks for external events and WebSockets to push updates to clients in real time.�
?? 8. Strong Signals vs Weak Signals
?? Choose Polling
- �Simple app�
- �Low frequency updates�
?? Choose Long-Polling
- �Need near real-time�
- �WebSockets not possible�
?? Choose WebSockets
- �Real-time interaction�
- �Chat / gaming / live feeds�
?? Choose Webhooks
- �Third-party integration�
- �Event-driven architecture�
?? Weak Signals
- �Real-time ? always WebSockets� ?
- �Integration ? polling APIs� ? (use webhooks)
?? 9. FAANG-Level Insights (Added)
?? 1. Backpressure Handling (WebSockets)
- Prevent overload from fast producers
?? 2. Connection Scaling
- Use load balancers + sticky sessions
?? 3. Retry Logic (Webhooks)
- Exponential backoff
?? 4. Hybrid Systems
- WebSockets + fallback to long-polling
?? Final Ultra-Short Summary
?? Golden Line
�Polling asks, long-polling waits, WebSockets stay connected, and webhooks push events.�
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