DVA-C02 Troubleshooting and Optimization Practice Question
A Lambda function processing SQS messages is failing with concurrency errors. The function is configured with reserved concurrency of 5. The SQS queue has a batch size of 10. What is the most effective way to prevent throttling?
⚠ Common exam trap
Candidates often confuse batch size with concurrency, thinking reducing batch size reduces load, but it actually increases invocation count and worsens throttling.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Increase the reserved concurrency to a higher value.
The function is throttling due to insufficient reserved concurrency. With a batch size of 10, each SQS batch triggers one invocation, but the function's reserved concurrency of 5 limits concurrent executions to 5. Increasing reserved concurrency allows more concurrent invocations to handle the SQS messages without throttling.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Reduce the batch size to 1 to spread out invocations.
Why it's wrong here
Reducing the batch size to 1 means the Lambda event source mapping will invoke the function more frequently to process the same volume of SQS messages. This increases the *rate* of invocations, making it *more likely* for the function to hit its concurrency limits and experience throttling, rather than effectively spreading out invocations. A smaller batch size requires more distinct invocations to clear the queue, exacerbating concurrency issues.
- ✗
Increase the Lambda function memory to get more concurrency.
Why it's wrong here
Increasing the Lambda function's memory allocation primarily enhances the CPU, network bandwidth, and temporary disk space available to *each individual execution* of the function. While this can improve the performance and reduce the duration of a single invocation, it does not directly increase the *total number of concurrent invocations* that Lambda allows for that specific function or across the entire account. Concurrency is a distinct resource managed separately from memory.
- ✓
Increase the reserved concurrency to a higher value.
Why this is correct
Increasing the reserved concurrency for the Lambda function dedicates a specific number of concurrent execution slots exclusively to that function. This guarantees that the function will always have that many concurrent instances available, preventing it from being throttled by the overall account-level concurrency limit or by other functions consuming available capacity. By reserving more concurrency, the function can process a higher parallel load from SQS without interruption, directly addressing throttling issues.
- ✗
Set the SQS queue's concurrency limit to match the Lambda reserved concurrency.
Why it's wrong here
Amazon SQS is a message queuing service and does not inherently possess a 'concurrency limit' setting that can be configured on the queue itself. SQS simply stores messages and makes them available for consumers. The concurrency of processing SQS messages is managed by the Lambda event source mapping, which controls how many concurrent batches of messages Lambda attempts to process from the queue, not by any SQS queue-level setting.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DVA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DVA-C02 exam.