AWS Error: SQS Long Polling vs Short Polling

#aws#sqs#devops#cloud

Why your queue looks empty — or your bill Is high

Problem

Your application reads from an Amazon SQS queue, but:

• Messages arrive with noticeable delay
• The queue often looks empty even though producers are sending messages
• Your SQS bill shows a high number of empty receives
• Polling feels inefficient and unpredictable

Nothing appears “broken,” yet performance and cost don’t line up with expectations.

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Clarifying the Issue

This is almost never a throughput problem.

It is almost always a polling configuration mismatch.

By default, SQS uses Short Polling, which:

• Returns immediately
• Often returns no messages
• Can miss messages temporarily
• Generates many empty receives

Long Polling changes this behavior entirely — but only if it’s explicitly enabled and supported by the client.

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Why It Matters

Polling strategy affects latency, reliability, and cost.

Short polling:

• Increases empty receives
• Increases API calls
• Increases cost
• Adds delay under light or bursty traffic

Long polling:

• Reduces empty receives
• Reduces API calls
• Improves responsiveness
• Lowers cost automatically

Many systems feel “slow” or “chatty” simply because they are polling incorrectly.

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Key Terms

• Short Polling – Default behavior where SQS returns immediately, often empty
• Long Polling – SQS waits (up to 20 seconds) for messages to arrive
• WaitTimeSeconds – How long SQS waits before returning a receive call
• Empty Receive – A ReceiveMessage call that returns no messages
• ReceiveMessageWaitTimeSeconds – Queue-level long polling setting
• Client Read Timeout – How long the HTTP client waits before giving up

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Steps at a Glance

1. Understand the difference between short and long polling
2. Check queue-level long polling settings
3. Check consumer-level polling configuration
4. Verify client-side HTTP timeouts
5. Identify the empty receive cost trap

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Detailed Steps

Step 1: Understand Short Polling (The Default Trap)

Short polling returns immediately, even if no messages are available.

This means:

• SQS checks a subset of servers
• Messages may exist but not be returned
• Consumers spin aggressively
• Empty receives accumulate quickly

❌ “Empty means the queue is empty”
✅ “Empty often means polling too fast”

Short polling is fast — but inefficient.

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Step 2: Understand Long Polling (The Fix)

Long polling tells SQS:

“Wait until a message arrives, or until the timeout expires.”

With long polling:

• SQS waits up to 20 seconds
• Messages are returned as soon as they arrive
• Empty receives drop dramatically
• Latency improves under low traffic

✅ Long polling improves performance and reduces cost
❌ It is not enabled by default everywhere

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Step 3: Check the Queue-Level Setting

SQS supports long polling at the queue level.

The setting:

• ReceiveMessageWaitTimeSeconds

If set to:

• 0 → Short polling
• 1–20 → Long polling

Action

• Open queue settings
• Set ReceiveMessageWaitTimeSeconds to 20 seconds
• This becomes the default for all consumers

✅ Queue-level long polling protects you even if consumers forget to configure it

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Step 4: Check Consumer Configuration and Timeouts

Most SDKs allow polling configuration per request.

If the consumer explicitly sets:

• WaitTimeSeconds = 0

…it overrides the queue default and forces short polling.

But there is a second, more dangerous trap.

The Timeout Mismatch

If you enable long polling (e.g., 20 seconds), but your client’s HTTP read timeout is shorter (e.g., 10–15 seconds), the client will error before SQS responds.

❌ SQS waits 20s, client times out at 15s → error loop
✅ Client timeout > SQS wait time

Action

• Audit consumer code and SDK configuration
• Verify HTTP / socket read timeouts
• Ensure Client Timeout > WaitTimeSeconds (e.g., 30s client, 20s SQS)

This is the most common failure after “optimizing” for long polling.

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Step 5: Understand the Empty Receive Cost Trap

SQS charges per ReceiveMessage request, not per message returned.

Short polling causes:

• High request volume
• Many empty responses
• Unexpected cost spikes

Long polling:

• Reduces API calls
• Collapses idle polling
• Cuts empty receives dramatically

❌ High cost + empty queue ≠ bug
✅ High cost + empty queue = short polling

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Pro Tips

• Long polling should be the default in almost all systems
• Set long polling at the queue level for safety
• ❌ Client timeouts shorter than wait time will break long polling
• Empty receives are a cost signal, not noise
• Monitor NumberOfEmptyReceives

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Conclusion

When an SQS queue looks empty — or costs more than expected — the problem is usually how you’re polling, not what you’re sending.

Short polling is fast but wasteful.
Long polling is efficient, responsive, and cheaper.

Once you:

• Enable long polling
• Align client timeouts
• Remove short-poll overrides

…the queue behaves predictably and efficiently.

This Fix-It isn’t about tuning performance.
It’s about aligning clients with how SQS actually works.

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Aaron Rose is a software engineer and technology writer at tech-reader.blog and the author of Think Like a Genius.