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Data Operations and Support →mediumMultiple ChoiceObjective-mapped

DEA-C01 Data Operations and Support Practice Question

This DEA-C01 practice question tests your understanding of data operations and support. 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 Amazon S3 to store log files from multiple sources. The logs are partitioned by year, month, day, and hour. A data engineer uses Amazon Athena to query the logs. Recently, users have reported that queries are taking longer than expected. The engineer notices that many queries are scanning large amounts of data even when filtering on partition columns. The total data size is 10 TB, and the average query scans 2 TB. The partition columns are properly defined in the table schema. What is the most likely cause of the slow queries?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

A
The number of partitions is too large, causing Athena to spend time listing partitions.
Why wrong: A large number of partitions can cause overhead but does not increase the amount of data scanned.
B
The table is not partitioned, or the partitions are not properly defined in the table DDL.
Without proper partitions, Athena scans the entire dataset, causing high scan volumes and slow queries.
C
The log files are stored in compressed format (e.g., gzip), which increases the amount of data scanned.
Why wrong: Compression reduces the amount of data scanned by Athena.
D
The log files are stored in CSV format instead of columnar formats like Parquet.
Why wrong: While columnar formats are more efficient, the primary issue is partition pruning.

Full breakdown with real-world context →

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 table is not partitioned, or the partitions are not properly defined in the table DDL.

Option B is the most likely cause. Although the partition columns are defined in the table schema, partition pruning in Athena only works if the data is stored in a matching Hive-style partition layout (e.g., s3://bucket/year=2024/month=01/day=01/hour=12/). If the S3 prefix does not follow this pattern, Athena must scan all partitions, resulting in large data scans. Option A is incorrect because a large number of partitions can cause slow metadata operations but does not inherently increase the amount of data scanned; partition pruning still applies. Option C is incorrect because compressed files reduce the amount of data scanned, not increase it. Option D is incorrect because while columnar formats like Parquet improve query performance by reading only necessary columns, they do not affect partition pruning; the issue here is that partitions are not being pruned.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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 partitions is too large, causing Athena to spend time listing partitions.
Why it's wrong here
A large number of partitions can cause overhead but does not increase the amount of data scanned.
✓
The table is not partitioned, or the partitions are not properly defined in the table DDL.
Why this is correct
Without proper partitions, Athena scans the entire dataset, causing high scan volumes and slow queries.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The log files are stored in compressed format (e.g., gzip), which increases the amount of data scanned.
Why it's wrong here
Compression reduces the amount of data scanned by Athena.
✗
The log files are stored in CSV format instead of columnar formats like Parquet.
Why it's wrong here
While columnar formats are more efficient, the primary issue is partition pruning.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

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.

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

What to study next

Got this wrong? Here's your next step.

Identify which DEA-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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FAQ

Questions learners often ask

What does this DEA-C01 question test?

Data Operations and Support — This question tests Data Operations and Support — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The table is not partitioned, or the partitions are not properly defined in the table DDL. — Option B is the most likely cause. Although the partition columns are defined in the table schema, partition pruning in Athena only works if the data is stored in a matching Hive-style partition layout (e.g., s3://bucket/year=2024/month=01/day=01/hour=12/). If the S3 prefix does not follow this pattern, Athena must scan all partitions, resulting in large data scans. Option A is incorrect because a large number of partitions can cause slow metadata operations but does not inherently increase the amount of data scanned; partition pruning still applies. Option C is incorrect because compressed files reduce the amount of data scanned, not increase it. Option D is incorrect because while columnar formats like Parquet improve query performance by reading only necessary columns, they do not affect partition pruning; the issue here is that partitions are not being pruned.

What should I do if I get this DEA-C01 question wrong?

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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