DVA-C02 Troubleshooting and Optimization Practice Question
A company's application uses Amazon S3 to store user-uploaded images. Users report that recently uploaded images are sometimes not immediately available for viewing. The application uses S3 Event Notifications to trigger a Lambda function that processes images and stores metadata in DynamoDB. What is the MOST likely cause of the delay?
⚠ Common exam trap
DVA-C02 often tests whether candidates still believe S3 is eventually consistent for new writes (it has been strongly consistent since 2020) and whether they understand that event notifications are asynchronous, so the trap is blaming cold starts or DynamoDB throttling instead of the notification latency and polling race.
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
✓
S3 Event Notifications may have a slight delay, and the application polls for the processed image before the notification triggers Lambda.
S3 Event Notifications are delivered asynchronously and can take seconds to minutes to reach Lambda, so if the application polls for the processed image or metadata immediately after upload, it may query before Lambda has run. This race condition between the upload and the notification-driven processing is the most likely cause of the intermittent delay.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Lambda function has a cold start that adds several seconds to processing time.
Why it's wrong here
Lambda cold starts introduce a small amount of latency, typically ranging from hundreds of milliseconds to a few seconds, depending on the runtime, package size, and invocation frequency. While this delay can impact highly sensitive real-time applications, it is generally not "several seconds" in a way that would cause a significant, perceived unavailability for a typical image processing workflow. This sub-second to low-single-digit-second overhead is usually absorbed within the overall processing time and not the primary reason for an image appearing "not immediately available" to an application that might be polling.
- ✗
S3 is eventually consistent for new object writes, so the object may not be immediately available.
Why it's wrong here
Amazon S3 provides strong read-after-write consistency for new object PUTS in all AWS Regions. This means that once an object is successfully uploaded to S3, any subsequent GET request for that object will immediately return the latest version. Therefore, the premise that new object writes are eventually consistent and thus unavailable for immediate retrieval is factually incorrect, making this option an invalid cause for the observed delay.
- ✓
S3 Event Notifications may have a slight delay, and the application polls for the processed image before the notification triggers Lambda.
Why this is correct
S3 Event Notifications are delivered asynchronously and on a best-effort basis, meaning there can be an inherent, variable delay between an object being uploaded and the corresponding Lambda function being invoked. If the application immediately polls for the *processed* image after the initial upload, it creates a race condition where the polling might occur before the S3 event has triggered the Lambda function to process the image, or before the processing itself has completed and the processed image is stored. This asynchronous nature and potential latency in event delivery are a common cause for such perceived delays.
- ✗
DynamoDB has insufficient read capacity causing throttling on metadata retrieval.
Why it's wrong here
This option suggests that DynamoDB's read capacity is insufficient for metadata retrieval, leading to throttling. However, the problem statement focuses on the *processed image* not being immediately available after upload, implying a delay in the image *processing workflow* itself. While DynamoDB throttling can cause delays in data access, it's less likely to be the primary bottleneck for the *availability of a processed image* unless the application is specifically failing to retrieve the *location* of the processed image due to metadata read issues, which is a secondary effect. For typical metadata access patterns, DynamoDB's provisioned or on-demand capacity usually handles reads efficiently without throttling unless severely misconfigured.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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