The correct answer is to create a secondary index on the order_date column. This index allows MySQL to perform a range scan for report queries that aggregate data by date, drastically reducing the number of rows scanned compared to a full table scan, which directly improves report performance on RDS MySQL with an index on date column. The existing primary key on order_id remains untouched, so OLTP queries filtering by that column continue to use the clustered index without degradation. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of index design trade-offs—specifically, that a secondary index accelerates read-heavy reporting while adding only minimal write overhead. A common trap is assuming a composite index on (order_id, order_date) would help, but that would bloat the index and fail to optimize date-range scans. Memory tip: think of the primary key as your house address for quick delivery, and the date index as a zip-code filter for bulk mail—separate tools for separate jobs.
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 uses Amazon RDS for MySQL to store e-commerce order data. The orders table has millions of rows and is frequently queried by order_id. The company also runs periodic reports that aggregate data by order_date. The reports are slow. The database has a primary key on order_id. The company needs to improve report performance without affecting OLTP queries. Which design change should be made?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a secondary index on order_date.
Creating a secondary index on order_date allows MySQL to quickly locate rows matching the report's date range without scanning the entire table, significantly improving aggregation performance. This index is separate from the primary key on order_id, so OLTP queries that filter by order_id remain unaffected. The index provides a balanced approach: it accelerates read-heavy reporting while adding minimal overhead to write operations.
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.
✓
Create a secondary index on order_date.
Why this is correct
A secondary index on order_date speeds up date-based aggregations without impacting OLTP queries.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Upgrade to a larger instance type.
Why it's wrong here
Hardware upgrade may help but is not a targeted optimization.
✗
Create a read replica and run reports on the replica.
Why it's wrong here
This offloads reporting but does not improve the performance of the queries themselves.
✗
Partition the table by order_date.
Why it's wrong here
Partitioning can help with data management but may not improve aggregation queries without proper indexing.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a read replica (Option C) solves all performance issues, but without an appropriate index, the replica still performs full table scans, making the reports slow regardless of where they run.
Detailed technical explanation
How to think about this question
In MySQL, secondary indexes are implemented as B+ trees that store the indexed column(s) and a pointer to the primary key. When a query filters by order_date, the index allows MySQL to perform an index range scan, reading only the relevant leaf nodes and then fetching the corresponding rows via the primary key. Without this index, MySQL would perform a full table scan, reading millions of rows and aggregating them in memory, which is CPU- and I/O-intensive. The choice of a secondary index over partitioning is deliberate: indexes are simpler to manage, do not require schema changes that affect all queries, and are fully supported by MySQL's optimizer for both point lookups and range scans.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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: Create a secondary index on order_date. — Creating a secondary index on order_date allows MySQL to quickly locate rows matching the report's date range without scanning the entire table, significantly improving aggregation performance. This index is separate from the primary key on order_id, so OLTP queries that filter by order_id remain unaffected. The index provides a balanced approach: it accelerates read-heavy reporting while adding minimal overhead to write operations.
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.
Are there clue words in this question I should notice?
Yes — watch for: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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