The answer is to use S3 Event Notifications to trigger a Lambda function that checks file size and then moves the file to a 'ready' prefix. This approach is correct because it leverages an atomic two-phase write pattern: the forecasting model writes results to a staging prefix, and only after the Lambda confirms a complete, non-zero-byte file does it rename the object into the processing prefix, ensuring the downstream ETL job never sees an incomplete file. On the AWS Certified Data Engineer Associate DEA-C01 exam, this question tests your understanding of data integrity patterns in serverless architectures, often appearing as a trap where candidates mistakenly choose S3 Copy or S3 Select, which cannot detect zero-byte files. The key insight is that S3 Event Notifications fire on every PUT, but combining them with a Lambda size check and a rename operation guarantees atomicity. Memory tip: think “Stage, Check, Rename” — never let your ETL touch raw staging data.
DEA-C01 Data Operations and Support Practice Question
This DEA-C01 practice question tests your understanding of data operations and support. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company runs a time-series forecasting model that writes results to an S3 bucket every 5 minutes. A downstream ETL job reads this data, but sometimes fails because it encounters incomplete files (zero bytes). What is the MOST reliable way to ensure the ETL job only processes complete files?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use S3 Event Notifications to trigger a Lambda function that checks file size and then moves the file to a 'ready' prefix.
Option B is correct because S3 Event Notifications with a Lambda function can process only after a final PUT, and writing to a temporary prefix then renaming ensures atomicity. Option A is wrong because S3 Copy can't detect completeness. Option C is wrong because S3 Select still reads incomplete files. Option D is wrong because S3 Lifecycle policies manage lifecycle, not completeness.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Set an S3 Lifecycle policy to delete files smaller than 1 MB.
Why it's wrong here
Does not ensure completeness; some valid files may be small.
✗
Use S3 Copy to move files to a 'processed' folder after the ETL job reads them.
Why it's wrong here
Does not address incomplete files; the job may still read incomplete files.
✗
Configure S3 Select to query the files and only return rows if the file is complete.
Why it's wrong here
S3 Select cannot detect incomplete files; it will simply return partial data.
✓
Use S3 Event Notifications to trigger a Lambda function that checks file size and then moves the file to a 'ready' prefix.
Why this is correct
Lambda can verify completeness before moving, ensuring only complete files are processed.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which DEA-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Data Operations and Support — This question tests Data Operations and Support — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use S3 Event Notifications to trigger a Lambda function that checks file size and then moves the file to a 'ready' prefix. — Option B is correct because S3 Event Notifications with a Lambda function can process only after a final PUT, and writing to a temporary prefix then renaming ensures atomicity. Option A is wrong because S3 Copy can't detect completeness. Option C is wrong because S3 Select still reads incomplete files. Option D is wrong because S3 Lifecycle policies manage lifecycle, not completeness.
What should I do if I get this DEA-C01 question wrong?
Identify which DEA-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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This DEA-C01 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 DEA-C01 exam.
Question Discussion
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