The answer is to use 'document_id' as the sole partition key. This design is most efficient because DynamoDB’s GetItem operation provides O(1) lookup performance when you query directly by the partition key, and each document up to 400 KB fits comfortably within DynamoDB’s 400 KB item size limit. On the AWS Certified Database Specialty DBS-C01 exam, this scenario tests your understanding of primary key design for single-item access patterns, a common trap being the temptation to add a sort key or secondary index unnecessarily. Remember: if the access pattern is “retrieve by unique ID,” a simple partition key is all you need—no composite key or index required. Memory tip: “One ID, one key, one call.”
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 is designing a document storage system using Amazon DynamoDB. Each document is up to 400 KB and is identified by a unique 'document_id'. The access pattern is to retrieve a document by its ID. Which DynamoDB table design is MOST efficient?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use 'document_id' as the primary partition key (only).
Option B is correct because DynamoDB can store items up to 400 KB in a single table, and using 'document_id' as the sole partition key directly supports the access pattern of retrieving a document by its ID with a single GetItem call, which is the most efficient operation. No secondary index or composite key is needed, as the primary key alone provides O(1) lookup performance for this use case.
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.
✗
Use 'document_id' as the partition key and create a GSI on 'document_id'.
Why it's wrong here
Unnecessary index.
✓
Use 'document_id' as the primary partition key (only).
Why this is correct
Direct GetItem by partition key is most efficient.
Related concept
Read the scenario before looking for a memorised answer.
✗
Store documents in Amazon S3 and use DynamoDB to store metadata with a reference to S3.
Why it's wrong here
Not a DynamoDB-only design; question asks for DynamoDB table design.
✗
Use a composite key: partition key 'document_id' and sort key 'version'.
Why it's wrong here
Unnecessary sort key adds complexity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often overcomplicate the design by adding GSIs or composite keys, or default to S3 for large objects, when the item size is within DynamoDB's limit and the access pattern is simple key-value lookup.
Detailed technical explanation
How to think about this question
DynamoDB's item size limit is 400 KB, including attribute names and values, so a 400 KB document fits comfortably. Using a single partition key allows direct hash-based lookup, achieving consistent single-digit millisecond latency at any scale. In contrast, a GSI would require additional write capacity and eventual consistency, while S3 retrieval adds network latency and requires two separate calls (DynamoDB then S3).
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 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.
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: Use 'document_id' as the primary partition key (only). — Option B is correct because DynamoDB can store items up to 400 KB in a single table, and using 'document_id' as the sole partition key directly supports the access pattern of retrieving a document by its ID with a single GetItem call, which is the most efficient operation. No secondary index or composite key is needed, as the primary key alone provides O(1) lookup performance for this use case.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This DBS-C01 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DBS-C01 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.