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 DynamoDB to store IoT sensor data. Each sensor writes a record every second, and the application needs to query the last 24 hours of data for a specific sensor. The query must be very fast. Which table design and query pattern will minimize cost and latency?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use a composite primary key: partition key = sensor ID, sort key = timestamp
Using a composite primary key with sensor ID as partition key and timestamp as sort key allows efficient querying of latest data with a Query operation on the partition key and a sort key condition. Option B (GSI on timestamp) is wrong because it would be less efficient for querying a specific sensor. Option C (scan) is wrong because it is expensive and slow. Option D (LSI on timestamp) is wrong because the sort key can be used directly without an LSI.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 simple primary key (sensor ID) and scan the table filtering by timestamp
Why it's wrong here
Scan is expensive and slow for large tables.
✓
Use a composite primary key: partition key = sensor ID, sort key = timestamp
Why this is correct
This allows efficient range queries on timestamp for a sensor.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Use a composite primary key: partition key = timestamp, sort key = sensor ID
Why it's wrong here
This would scatter data across partitions but still require a scan for a sensor.
✗
Use a simple primary key (sensor ID) and a global secondary index on timestamp
Why it's wrong here
GSI adds cost and querying by sensor ID then filtering by timestamp is less efficient.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DBS-C01 NAT questions on configuration and troubleshooting.
Workload-Specific Database Design — This question tests Workload-Specific Database Design — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Use a composite primary key: partition key = sensor ID, sort key = timestamp — Using a composite primary key with sensor ID as partition key and timestamp as sort key allows efficient querying of latest data with a Query operation on the partition key and a sort key condition. Option B (GSI on timestamp) is wrong because it would be less efficient for querying a specific sensor. Option C (scan) is wrong because it is expensive and slow. Option D (LSI on timestamp) is wrong because the sort key can be used directly without an LSI.
What should I do if I get this DBS-C01 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DBS-C01 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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