C100DBA Philosophy and Features Practice Question
Which feature of MongoDB allows it to maintain data consistency during primary node failure?
⚠ Common exam trap
Candidates confuse automatic failover with sharding or manual recovery. They often mistake the purpose of replica sets for load balancing rather than high availability and data consistency.
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
✓
Automatic failover via replica set elections.
MongoDB uses replica sets to ensure high availability. When a primary node becomes unavailable, the remaining nodes in the replica set conduct an election to select a new primary. This process is governed by the consensus algorithm, ensuring that only a node with the most up-to-date data can become the new primary, thereby preventing data loss and maintaining the consistency of the cluster during automated failover scenarios.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Manual shard intervention by the administrator.
Why it's wrong here
Manual intervention is not the primary way MongoDB ensures consistency. Replica sets are designed to be self-healing, utilizing automated elections to restore service. Requiring manual intervention would negate the benefits of a distributed system designed for high availability and minimal operational downtime during outages.
- ✓
Automatic failover via replica set elections.
Why this is correct
Replica set elections are the core mechanism for handling failures. When a primary node fails, the secondary nodes automatically initiate an election to select a new primary. This ensures that the system continues to accept writes with minimal disruption, maintaining consistency across the distributed environment.
- ✗
The use of a secondary index for read-only access.
Why it's wrong here
While secondary nodes can handle read-only traffic, this is a performance feature, not a mechanism for maintaining consistency during failover. Consistency is maintained through the replication protocol, which synchronizes data across all nodes, not through the act of querying the secondary nodes.
- ✗
The mongos router forcing a global write lock.
Why it's wrong here
The mongos router does not enforce global locks during failover. MongoDB uses granular, document-level concurrency control in the WiredTiger engine. Global locks were eliminated in early versions to improve performance, and mongos is strictly a routing component for sharded clusters, not a lock manager.
About these practice questions
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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.