The answer is salting the join key, using a broadcast join for the smaller table, and splitting the transformation into multiple Glue job steps. These three actions directly address the root cause of the memory error by distributing skewed data across partitions, minimizing shuffle overhead, and reducing per-stage memory pressure. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of how to handle data skew in DynamicFrame joins without simply scaling resources—a common trap is choosing to increase DPUs, which masks the problem rather than fixing it. Remember the mnemonic “SBS”: Salt, Broadcast, Split—each technique targets a specific failure point in skewed joins, making your Glue jobs stable and efficient.
DEA-C01 Data Ingestion and Transformation Practice Question
This DEA-C01 practice question tests your understanding of data ingestion and transformation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company uses AWS Glue to run ETL jobs that transform data from Amazon S3 (Parquet) into a denormalized format for Amazon Redshift. The Glue job uses the DynamicFrame API. The job is failing with a 'MemoryError' when performing a join operation. The data is skewed on the join key. Which THREE actions can reduce memory usage and improve job stability? (Choose THREE.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a broadcast join if one of the tables is small enough.
Options B, C, and D are correct. Salting the join key distributes skew, using broadcast join for a smaller table reduces shuffle, and splitting the job into multiple steps reduces memory per stage. Option A is wrong because increasing DPUs may help but is not a targeted solution. Option E is wrong because repartitioning does not fix skew and may increase overhead.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 broadcast join if one of the tables is small enough.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DEA-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Data Ingestion and Transformation — This question tests Data Ingestion and Transformation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Use a broadcast join if one of the tables is small enough. — Options B, C, and D are correct. Salting the join key distributes skew, using broadcast join for a smaller table reduces shuffle, and splitting the job into multiple steps reduces memory per stage. Option A is wrong because increasing DPUs may help but is not a targeted solution. Option E is wrong because repartitioning does not fix skew and may increase overhead.
What should I do if I get this DEA-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DEA-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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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.
Question Discussion
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