187. SQS - Long Polling

Amazon SQS Long Polling is a technique that allows consumers to wait for messages to arrive instead of continuously polling the queue. This reduces API calls, lowers costs, and minimizes latency in message retrieval.

1. Understanding Long Polling vs. Short Polling

🔹 Short Polling (Default Behavior)

When a consumer requests messages from the queue, it immediately returns a response even if the queue is empty.
If no messages are available, the API call returns an empty response.
Requires frequent polling, leading to higher costs and increased API calls.

🔹 Long Polling (Recommended Approach)

Instead of returning immediately, the request waits (up to 20 seconds) for a message to arrive.
If a message is available, it is delivered immediately.
Reduces API requests, lowering costs.
Minimizes message retrieval latency by delivering messages as soon as they arrive.

Feature	Short Polling 🚫	Long Polling ✅
API Call Frequency	Frequent requests (higher cost)	Fewer requests (lower cost)
Response Time	Immediate, even if no messages	Waits for messages, reducing empty responses
Cost Efficiency	Higher cost due to repeated polling	Lower cost with fewer API calls
Latency	Potential lag in message processing	Faster message delivery

2. How Long Polling Works

1️⃣ Consumer polls the SQS queue using the ReceiveMessage API.

2️⃣ If messages are available, they are immediately returned.

3️⃣ If no messages are in the queue, the request waits (up to 20 seconds) for new messages.

4️⃣ As soon as a message arrives, it is sent to the consumer immediately.

📌 Example Use Case: