MLS-C01 AWS Glue Crawler Practice Question
A company uses AWS Glue to catalog data in S3. Data is partitioned by year, month, day. The Glue crawler runs daily but sometimes misses new partitions. What should be done to ensure all partitions are cataloged?
⚠ Common exam trap
The trap is that candidates may confuse partition indexing (which optimizes queries on already-cataloged partitions) with automatic partition discovery. The correct solution is to adjust the crawler's update behavior to scan all partitions, not to rely on indexing for cataloging.
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
✓
Configure the crawler to update all partitions on each run.
Configuring the Glue crawler to 'update all partitions on each run' forces the crawler to scan the entire S3 path and register any new partitions it finds, even if the partition structure hasn't changed. This ensures all missed partitions are cataloged. Partition indexing (D) improves query performance by creating an index over existing partitions, but does not automatically discover new partitions.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use a custom classifier to detect partition patterns.
Why it's wrong here
Custom classifiers are for interpreting file formats or schemas, not for ensuring all partitions are cataloged.
- ✗
Increase the crawler schedule to run every hour.
Why it's wrong here
Increasing crawler frequency reduces the time delay but does not guarantee that a missed partition will be found if the crawler does not scan all partitions.
- ✓
Configure the crawler to update all partitions on each run.
Why this is correct
Configuring the crawler to update all partitions on each run ensures that the crawler scans the entire dataset and registers any new or missed partitions.
- ✗
Enable partition indexing in the Glue table properties.
Why it's wrong here
Partition indexing improves query performance by creating an index on existing partitions, but does not automatically discover or catalog new 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 |
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