- A
Use a find operation with the $or operator on the _id field.
Why wrong: $or is less efficient than $in for the same field.
- B
Use a scan operation with a filter on the _id field.
Why wrong: Scan reads all documents, which is inefficient.
- C
Use a find operation with the $in operator on the _id field.
Uses index on _id efficiently.
- D
Issue multiple get operations in parallel.
Why wrong: Multiple round trips increase latency.
Question 1,452 of 1,730
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 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?
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.
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 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 $in operator on the _id field.
Why this is correct
Uses index on _id efficiently.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Issue multiple get operations in parallel.
Why it's wrong here
Multiple round trips increase latency.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume parallel `get` operations (Option D) are fastest because they think concurrency equals speed, but they overlook the overhead of multiple network round trips and the fact that DocumentDB's `$in` operator performs a single index seek for all IDs, which is far more efficient under load.
Detailed technical explanation
How to think about this question
Under the hood, DocumentDB stores documents in a clustered index on `_id`, so `$in` translates to a single B-tree traversal that seeks each `_id` value directly, returning results in the order of the `_id` values in the array. This is similar to MongoDB's behavior, where `$in` on `_id` is optimized to avoid multiple round trips and can be more efficient than `$or` even when both use indexes, because `$or` may merge multiple index scans. In real-world scenarios, retrieving 100 documents with `$in` on `_id` can be 10x faster than 100 parallel `get` operations due to reduced latency and connection pooling overhead.
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.
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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: 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.
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.
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Last reviewed: Jul 4, 2026
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