MLS-C01 Data Engineering Practice Question
A data pipeline uses AWS Glue to crawl an S3 bucket and create a table in the AWS Glue Data Catalog. The data is in Parquet format with partitions by date. After a new partition is added to S3, the crawler runs but the new partition is not reflected in the table. What is the most likely cause?
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 new partition folder does not follow the Hive-style partition naming convention expected by the crawler.
The most likely cause is that the new partition folder does not follow the Hive-style partition naming convention expected by the crawler. AWS Glue crawlers expect partition directories to be named in the format key=value (e.g., date=2023-01-01). If the partitions are named differently, the crawler will not recognize them as partitions. Option A is incorrect because Glue crawlers do not require Lambda triggers. Option B is incorrect because schema mismatch would cause a different error, not just missing partitions. Option D is incorrect because while there is a limit on partitions, it is high enough that 'too many partitions' is less likely than a naming issue.
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 crawler requires an AWS Lambda trigger to be configured for new partitions.
Why it's wrong here
Glue crawlers do not need Lambda triggers; they can run on schedule.
- ✗
The Parquet schema in the new partition does not match the existing table schema.
Why it's wrong here
Glue crawlers can merge schemas if configured, but the partition would still be added.
- ✓
The new partition folder does not follow the Hive-style partition naming convention expected by the crawler.
Why this is correct
Glue crawlers require partition folders to follow the key=value pattern to automatically detect partitions.
- ✗
The S3 bucket has too many partitions, exceeding the Glue crawler limit.
Why it's wrong here
Glue crawlers support up to 10 million partitions.
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 by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This MLS-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 MLS-C01 exam.