DEA-C01 Data Operations and Support Practice Question
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 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
✓
Use S3 Event Notifications to trigger a Lambda function that checks file size and then moves the file to a 'ready' prefix.
S3 Event Notifications can trigger a Lambda function upon object creation, which can check the file size (e.g., > zero bytes) and then copy the file to a 'ready' prefix, ensuring the ETL job only processes complete files. Option A is wrong because an S3 Lifecycle policy can delete small files but does not prevent the ETL from reading incomplete files. Option B is wrong because S3 Copy does not verify completeness. Option C is wrong because S3 Select still reads the file even if it is incomplete; it doesn't guarantee completeness.
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
Lifecycle policies delete objects asynchronously on a schedule and cannot distinguish a zero-byte file still being written from a finished one, so the ETL job may still read incomplete data. Lifecycle rules are correct for cost-driven expiry or storage-class transitions, not write-completion signalling.
- ✗
Use S3 Copy to move files to a 'processed' folder after the ETL job reads them.
Why it's wrong here
Copying after reading does not prevent the ETL job from encountering a zero-byte file mid-write; the failure occurs before the move. Post-processing archiving is appropriate for retaining or relocating already-consumed objects, not for gating reads on write completion.
- ✗
Configure S3 Select to query the files and only return rows if the file is complete.
Why it's wrong here
S3 Select filters rows within a single object's content; it cannot detect that an object is still being written, so a zero-byte or partial file simply returns no rows rather than blocking the ETL. It is designed for retrieving subsets of columns from complete objects, which would be correct for reducing data transfer, not for coordinating write completion.
- ✓
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
S3 Event Notifications fire on object creation, letting a Lambda verify the object is non-zero before relocating it to a ready prefix. The ETL job then reads only that prefix, so it never encounters the zero-byte partial writes.
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
Related to this question
About these practice questions
This DEA-C01 question is part of Courseiva's 1,321-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.