DBS-C01 Workload-Specific Database Design Practice Question
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?
⚠ Common exam trap
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.
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
✓
Use 'document_id' as the primary partition key (only).
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.
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.
- ✗
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.
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