MLS-C01 Data Engineering Practice Question
Network Topology
A data engineer runs the above CLI command and sees that the bucket contains many small Parquet files (1 MB each) under the prefix. When querying this data with Athena, the query performance is poor and costs are high. Which approach would MOST improve performance and reduce cost?
⚠ Common exam trap
A common mix-up: candidates think adding more partitions always improves query performance, but in this scenario with many tiny files, more partitions would exacerbate the small-file problem and increase Athena's overhead.
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
✓
Consolidate the small files into fewer, larger Parquet files
C is correct because consolidating many small Parquet files into fewer, larger files (e.g., 128–256 MB each) reduces the overhead of Amazon Athena's file listing and metadata operations, and improves compression and predicate pushdown efficiency. Parquet is a columnar format optimized for analytics, so keeping it while reducing file count directly addresses the root cause of poor performance and high cost.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Convert the files to JSON format
Why it's wrong here
JSON is also not columnar and can be larger.
- ✗
Convert the files to CSV format
Why it's wrong here
CSV is not columnar and may increase scan size.
- ✓
Consolidate the small files into fewer, larger Parquet files
Why this is correct
Fewer, larger files reduce overhead and improve compression.
- ✗
Add more partitions by including hour in the prefix
Why it's wrong here
More partitions could lead to even more small files.
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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.