MLS-C01 Data Engineering Practice Question
A data engineer uses AWS Glue to run ETL jobs that transform data from JSON to Parquet. The job runs successfully but takes 30 minutes longer than expected. CloudWatch metrics show high memory utilization and disk spills. What is the most likely cause?
⚠ Common exam trap
It's easy for candidates to assume high memory usage means insufficient resources (DPUs) and choose Option A, but the real culprit is data skew causing inefficient resource utilization, not a lack of total compute capacity.
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 data is skewed and not evenly distributed across partitions
High memory utilization and disk spills in AWS Glue indicate that the data is not evenly distributed across partitions, causing some executors to handle a disproportionate amount of data. This data skew leads to excessive spilling to disk as memory is exhausted, which significantly slows down the job. Option D directly addresses this root cause, as skewed data prevents efficient parallel processing.
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 number of DPUs is too low
Why it's wrong here
While low DPUs could cause spills, the symptom of high memory utilization suggests skew rather than insufficient resources.
- ✗
The sink bucket has insufficient I/O throughput
Why it's wrong here
S3 scales automatically; I/O is rarely a bottleneck for write operations.
- ✗
The source data format is too large
Why it's wrong here
Large files are expected and Glue handles them; the issue is distribution.
- ✓
The data is skewed and not evenly distributed across partitions
Why this is correct
Data skew causes some tasks to take longer, leading to spills and increased runtime.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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