C100DBA CRUD Operations Practice Question
A MongoDB 6.0 replica set has a collection called orders with the default read concern. Users occasionally see an order document that still shows status "pending" even though a separate application thread just updated it to "shipped" and received an acknowledgment. The update used default write concern and targeted a single document by _id. Which read concern should you set on the read operation to guarantee the read returns data acknowledged by a majority of replica set members?
⚠ Common exam trap
The trap here is assuming that a default acknowledged write immediately becomes visible to all reads, when in fact only majority read concern guarantees that majority-acknowledged data is returned.
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
✓
readConcern: "majority"
The symptom is a stale read after an acknowledged single-document update in a replica set. Majority read concern ensures the read only returns data that a majority of members have acknowledged, so the newly committed "shipped" status becomes visible. Local and available provide no such guarantee, and snapshot is aimed at multi-document consistency rather than this single-document visibility problem.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
readConcern: "snapshot"
Why it's wrong here
Snapshot read concern provides a consistent point-in-time view across multiple documents, but it is designed primarily for multi-document transactions and causally consistent sessions. Used alone on a simple find, it does not by itself guarantee that a just-acknowledged single-document update is reflected, so it does not solve the stale-read symptom described.
- ✗
readConcern: "available"
Why it's wrong here
Available read concern is intended for sharded collections and returns data without guaranteeing consistency or majority acknowledgment. It offers the weakest visibility guarantees and would still permit the stale "pending" value to be returned. It is inappropriate when the requirement is to see majority-acknowledged data.
- ✗
readConcern: "local"
Why it's wrong here
Local read concern returns data from the queried replica set member without waiting for a majority acknowledgment. In this scenario it still allows the stale "pending" value to be observed after the update thread returns, because the primary's write has not necessarily been replicated to a majority. It does not provide the majority-acknowledged visibility the users need.
- ✓
readConcern: "majority"
Why this is correct
Majority read concern returns only data that has been acknowledged by a majority of replica set members. Once the update thread receives default acknowledgment, a subsequent majority read is guaranteed to see the committed "shipped" state, eliminating the stale "pending" observation. This is exactly the guarantee needed for the described symptom.
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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 C100DBA 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 C100DBA exam.