DEA-C01 Data Operations and Support Practice Question
A data engineer is using Amazon Athena to query Parquet data in Amazon S3. Queries are slow and scan more data than expected. The data is partitioned by year/month/day in S3, but the AWS Glue Data Catalog table has no partition metadata. Which action will improve query performance and reduce data scanned?
⚠ Common exam trap
The trap here is assuming that file format or compression changes are needed, when the real issue is that partition metadata is absent from the Data Catalog.
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
✓
Run MSCK REPAIR TABLE or use AWS Glue Crawler to populate partition metadata in the Data Catalog.
Athena relies on the AWS Glue Data Catalog to know which partitions exist. If the table has no partition metadata, Athena treats the entire S3 prefix as one dataset and scans all files. Registering partitions via MSCK REPAIR TABLE or a Glue Crawler enables partition pruning, so queries only read the relevant partitions. This reduces both data scanned and query latency.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Run MSCK REPAIR TABLE or use AWS Glue Crawler to populate partition metadata in the Data Catalog.
Why this is correct
Without partition metadata, Athena cannot prune partitions and must scan the entire table location. Running MSCK REPAIR TABLE adds partitions to the Glue Data Catalog, or a Glue Crawler can discover and register them. Once partitions are registered, Athena can skip irrelevant partitions, reducing data scanned and improving speed.
- ✗
Enable Athena query result reuse and set a longer result retention period.
Why it's wrong here
Query result reuse helps only when identical queries are rerun within the retention window. It does not address the underlying issue of scanning all partitions for new queries. The performance problem is caused by missing partition metadata, so caching results does not reduce data scanned for first-time or varied queries.
- ✗
Increase the number of Athena workgroups and set a higher data usage control limit.
Why it's wrong here
Workgroups manage query access and cost controls, not performance. Raising the data usage control limit allows more data to be scanned but does not reduce it. This option does not address the missing partition metadata, which is the root cause of excessive scanning.
- ✗
Convert the data to CSV and use a SerDe that supports compression.
Why it's wrong here
Converting to CSV would increase data scanned because CSV is row-based and not columnar. Parquet already provides columnar storage and compression, which reduces scanned data. The problem is missing partition metadata, not file format, so this change would worsen performance.
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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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
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.