C100DEV Drivers, Tools, Transactions, and Search Practice Question
A developer is building a Node.js application that connects to a MongoDB replica set. The application must ensure that every read operation sees a consistent snapshot of the data, even if other clients are concurrently modifying documents. Which read concern level should be used for these reads?
⚠ Common exam trap
Candidates often confuse durability guarantees (majority) with snapshot isolation, which are distinct properties.
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
✓
"snapshot"
The "snapshot" read concern provides a consistent snapshot of the data across multiple documents, ensuring that the application sees a stable view even with concurrent writes. Other read concerns like "local", "majority", or "available" do not offer this snapshot isolation, so they are unsuitable for the stated requirement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
"snapshot"
Why this is correct
The "snapshot" read concern returns data as it appeared at a specific point in time, providing a consistent snapshot across multiple documents. This is exactly what the application needs to avoid seeing partial updates from concurrent writes. It is available for replica sets and sharded clusters and is often used with transactions or for consistent reads.
- ✗
"local"
Why it's wrong here
The "local" read concern returns data from the node with the least latency, without guaranteeing that the data has been replicated to a majority of nodes. It does not provide a consistent snapshot across multiple documents, so concurrent writes could cause the application to see partial or rolled-back data. This level is suitable for use cases where durability is not critical.
- ✗
"available"
Why it's wrong here
The "available" read concern is the default for reads against sharded collections and provides no consistency guarantees. It returns data from the shard without ensuring it has been replicated or that it represents a consistent snapshot. It is intended for low-latency reads where consistency is not required, so it does not meet the requirement.
- ✗
"majority"
Why it's wrong here
The "majority" read concern guarantees that the data read has been acknowledged by a majority of replica set members, providing durability. However, it does not guarantee a consistent snapshot across multiple documents; it only ensures that the data is durable. For snapshot isolation, a different read concern is needed.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official MongoDB exam blueprint
This C100DEV practice question is part of Courseiva's free MongoDB 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 C100DEV exam.