The correct answer is to set the sort key to the date column. This improves Redshift query performance by enabling range-restricted scans, where the columnar storage uses zone maps to skip entire blocks that fall outside the query’s date filter, dramatically reducing the number of rows scanned. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of how sort keys directly impact filter-heavy workloads on large fact tables—a common trap is confusing sort keys with distribution keys, but remember that sort keys optimize data ordering for range predicates, while distribution keys optimize data placement across nodes. For filter-heavy queries on a date column, a sort key is the most direct and cost-effective optimization because it minimizes I/O without requiring additional storage or node scaling. Memory tip: “Sort to skip, distribute to join”—if your query filters on a column, sort it first.
DBS-C01 Workload-Specific Database Design Practice Question
This DBS-C01 practice question tests your understanding of workload-specific database design. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 runs a reporting application on Amazon Redshift. The application queries a large fact table that is distributed by a key. The report queries filter on a date column. The report performance is slow. The database has 10 nodes. The company wants to improve query performance by optimizing the table design. Which design change should be made?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set the sort key to the date column.
Setting the sort key to the date column improves query performance by enabling range-restricted scans. When queries filter on a date column, Redshift uses zone maps to skip blocks that do not contain relevant data, drastically reducing the number of rows scanned. This is the most direct and cost-effective optimization for filter-heavy workloads on large fact tables.
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.
✓
Set the sort key to the date column.
Why this is correct
Sort keys enable efficient range filtering, improving query performance for date-based filters.
Related concept
Read the scenario before looking for a memorised answer.
✗
Increase the number of nodes in the cluster.
Why it's wrong here
Adding nodes may help parallelism but does not optimize the table design.
✗
Change the distribution style to ALL to avoid data redistribution.
Why it's wrong here
ALL distribution copies the table to all nodes, which is not ideal for large fact tables.
✗
Change the distribution style to KEY on the date column.
Why it's wrong here
Distributing by date may cause data skew if dates are not evenly distributed.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the purpose of distribution keys (for join co-location) with sort keys (for filter pruning), leading them to choose distribution changes (options C or D) instead of the correct sort key optimization.
Detailed technical explanation
How to think about this question
Redshift stores data in 1 MB blocks, and each block stores the minimum and maximum values of the sort key columns in zone maps. When a query includes a filter on the sort key, the query planner uses these zone maps to eliminate entire blocks from the scan, a process known as block-level pruning. For a fact table with billions of rows, this can reduce I/O by orders of magnitude compared to scanning all blocks. The sort key should be the column most frequently used in WHERE clauses, not the distribution key, which is optimized for join performance.
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.
TExam Day Tips
→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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Set the sort key to the date column. — Setting the sort key to the date column improves query performance by enabling range-restricted scans. When queries filter on a date column, Redshift uses zone maps to skip blocks that do not contain relevant data, drastically reducing the number of rows scanned. This is the most direct and cost-effective optimization for filter-heavy workloads on large fact tables.
What should I do if I get this DBS-C01 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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