DEA-C01 Data Operations and Support Practice Question
A company uses Amazon S3 to store log files from multiple applications. The logs are written in JSON format. A data engineer wants to use Amazon Athena to query these logs. The logs are stored in a bucket with the following structure: 's3://logs/app1/date=2021-01-01/'. The engineer creates an Athena table with partitions. However, when querying, Athena returns zero results for partitions that exist. The engineer has run MSCK REPAIR TABLE to add partitions. What is the most likely cause of the issue?
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
✓
The partition key name in the table definition does not match the S3 folder naming convention.
The most likely cause is that the partition key name in the Athena table definition does not match the S3 folder naming convention. When using MSCK REPAIR TABLE, Athena relies on the partition folder structure (e.g., 'date=2021-01-01') to automatically add partitions. If the table's partition key is named differently (e.g., 'dt' instead of 'date'), MSCK REPAIR will not recognize the folders and will not register the partitions, resulting in zero results. Option A is incorrect because MSCK REPAIR does not fail silently; it either adds partitions or reports none if the structure doesn't match. Option C is incorrect because Athena fully supports JSON format. Option D is incorrect because the bucket location does not affect partition registration; data can be queried in any bucket as long as the table points to it.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The MSCK REPAIR TABLE command failed silently.
Why it's wrong here
MSCK REPAIR TABLE reports errors rather than failing silently, so this misdiagnoses the symptom. It tempts engineers who distrust the command, yet the actual cause is partition projection or a key layout mismatch: Hive-style partitions must match the S3 prefix exactly for Athena to register them.
- ✓
The partition key name in the table definition does not match the S3 folder naming convention.
Why this is correct
This is the correct answer. The S3 folder structure uses 'date=' as the partition key prefix, so the Athena table must define a partition key named 'date' exactly. If it is named differently, MSCK REPAIR will not register those folders as partitions.
- ✗
The log files are in JSON format and Athena does not support JSON.
Why it's wrong here
Athena queries JSON through SerDe libraries such as OpenX JSON SerDe, so format is not the blocker. It tempts engineers seeing zero rows and blaming the data format, but the real issue lies in partition registration or prefix layout, not JSON support.
- ✗
The log files need to be copied to a different bucket in the same region.
Why it's wrong here
Athena reads S3 data in place, so relocating files to another bucket changes nothing about partition discovery. It tempts engineers assuming a regional or bucket-permission problem, yet zero results with existing partitions point to partition metadata or prefix structure, not object location.
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 |
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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.