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Workload-Specific Database Design →hardMultiple ChoiceObjective-mapped

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 social media analytics company uses Amazon DynamoDB as the primary data store for user session data. Each session record has a partition key of user_id (String) and a sort key of session_start_time (Number, epoch). The application often queries the most recent 10 sessions for a given user. The traffic pattern shows that 90% of reads are for the last 10 sessions, while 10% are for historical sessions. The table has a provisioned read capacity of 5000 RCU and consistently experiences throttled read requests during peak hours. The company wants to optimize read performance without changing the provisioned capacity. Which design change will MOST improve read performance for this workload?

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.

Question 1hardmultiple choice

Read the full NAT/PAT explanation →

A
Create a Global Secondary Index (GSI) with the same partition key and a sort key of session_start_time, but query with ScanIndexForward=false and Limit=10.
A GSI with the sort key reversed allows efficient retrieval of recent sessions using a single Query with ScanIndexForward=false and Limit=10.
B
Increase the provisioned read capacity to 10000 RCU to handle the peak load.
Why wrong: Increasing read capacity only addresses throughput but does not optimize the query pattern.
C
Enable DynamoDB Accelerator (DAX) with default settings to cache the most recent sessions.
Why wrong: DAX caches results but does not inherently retrieve the most recent sessions efficiently; it still requires the same Query pattern.
D
Configure Amazon ElastiCache for Redis as a read-through cache for session data.
Why wrong: ElastiCache adds a caching layer but does not optimize the DynamoDB query pattern for recent sessions.

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

✓

Create a Global Secondary Index (GSI) with the same partition key and a sort key of session_start_time, but query with ScanIndexForward=false and Limit=10.

Option A is correct because creating a GSI with the same partition key (user_id) and sort key (session_start_time) allows you to query with ScanIndexForward=false and Limit=10 to efficiently retrieve only the most recent 10 sessions per user. This avoids scanning all sessions for a user, reducing consumed read capacity and eliminating throttling without increasing provisioned RCU. The GSI also supports the 90% workload pattern by providing a targeted index that minimizes read unit consumption.

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 Global Secondary Index (GSI) with the same partition key and a sort key of session_start_time, but query with ScanIndexForward=false and Limit=10.
Why this is correct
A GSI with the sort key reversed allows efficient retrieval of recent sessions using a single Query with ScanIndexForward=false and Limit=10.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Increase the provisioned read capacity to 10000 RCU to handle the peak load.
Why it's wrong here
Increasing read capacity only addresses throughput but does not optimize the query pattern.
✗
Enable DynamoDB Accelerator (DAX) with default settings to cache the most recent sessions.
Why it's wrong here
DAX caches results but does not inherently retrieve the most recent sessions efficiently; it still requires the same Query pattern.
✗
Configure Amazon ElastiCache for Redis as a read-through cache for session data.
Why it's wrong here
ElastiCache adds a caching layer but does not optimize the DynamoDB query pattern for recent sessions.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often assume caching (DAX or ElastiCache) is the best solution for read-heavy workloads, but in this scenario the inefficiency is due to querying the base table without an index that supports efficient retrieval of the last N items, so a GSI with reversed sort order directly reduces read consumption without adding cache management overhead.

Detailed technical explanation

How to think about this question

When querying a DynamoDB table with a sort key, using ScanIndexForward=false on a GSI with the same partition key and sort key allows DynamoDB to read items in reverse order from the index, and the Limit parameter stops the query after retrieving exactly 10 items. This consumes only the read capacity for those 10 items (plus a small overhead), whereas a full scan of all sessions for a user could consume hundreds of read units. Under the hood, DynamoDB indexes store items sorted by sort key, so reverse-order queries are efficient and cost-effective.

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.

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FAQ

Questions learners often ask

What does this DBS-C01 question test?

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 Global Secondary Index (GSI) with the same partition key and a sort key of session_start_time, but query with ScanIndexForward=false and Limit=10. — Option A is correct because creating a GSI with the same partition key (user_id) and sort key (session_start_time) allows you to query with ScanIndexForward=false and Limit=10 to efficiently retrieve only the most recent 10 sessions per user. This avoids scanning all sessions for a user, reducing consumed read capacity and eliminating throttling without increasing provisioned RCU. The GSI also supports the 90% workload pattern by providing a targeted index that minimizes read unit consumption.

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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