DBS-C01 Workload-Specific Database Design Practice Question
A company is designing a document management system using Amazon DocumentDB. Each document is up to 10 MB. The application needs to retrieve multiple documents by their IDs in a single request. The IDs are known at query time. Which query pattern is most efficient?
⚠ Common exam trap
It's easy for candidates to assume parallel `get` operations (Option D) are fastest because they think concurrency equals speed, but they overlook the overhead of multiple network round trips and the fact that DocumentDB's `$in` operator performs a single index seek for all IDs, which is far more efficient under load.
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 a find operation with the $in operator on the _id field.
The `$in` operator on the `_id` field allows DocumentDB to use the primary key index directly, retrieving multiple documents in a single round trip with minimal overhead. This is the most efficient pattern because it leverages the clustered index on `_id` and avoids the performance penalty of multiple queries or full scans.
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 find operation with the $or operator on the _id field.
Why it's wrong here
$or is less efficient than $in for the same field.
- ✗
Use a scan operation with a filter on the _id field.
Why it's wrong here
Scan reads all documents, which is inefficient.
- ✓
Use a find operation with the $in operator on the _id field.
Why this is correct
Uses index on _id efficiently.
- ✗
Issue multiple get operations in parallel.
Why it's wrong here
Multiple round trips increase latency.
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