C100DBA Application Administration Practice Question
Which TWO of the following are essential for maintaining performance in a sharded cluster?
⚠ Common exam trap
Test-takers frequently select low cardinality fields like boolean status flags as good shard keys, completely misunderstanding how poor distribution creates severe cluster bottlenecks.
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
✓
Selecting a shard key with high cardinality.
A well-chosen shard key is the most critical factor for even data distribution, while monitoring chunks ensures that data remains balanced across the cluster. If the shard key is poorly chosen, some shards may become bottlenecks (hotspots), while others remain underutilized. Proper chunk management prevents excessive migration and ensures that query routers (mongos) efficiently route requests to the appropriate shards, maintaining overall system stability and throughput.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Selecting a shard key with high cardinality.
Why this is correct
High cardinality ensures that data is evenly distributed across shards. A low cardinality key leads to large chunks that cannot be split, causing hotspots where specific shards receive a disproportionate amount of traffic, leading to performance degradation and uneven resource utilization across the cluster.
- ✗
Hardcoding the shard primary in the application connection string.
Why it's wrong here
Applications should always connect via mongos instances, which abstract the cluster details. Hardcoding shard information is a dangerous practice that prevents the cluster from rebalancing data or handling failover, and it makes the application fragile and difficult to maintain as the cluster scales.
- ✓
Regularly monitoring and managing chunk splits.
Why this is correct
As data grows, chunks must split to keep the data distributed. Without proper balancing, the cluster will suffer from uneven distribution, where some shards become overwhelmed. Monitoring split and move operations ensures that the cluster effectively manages its workload and continues to scale as data accumulates.
- ✗
Disabling the balancer during all business hours.
Why it's wrong here
Disabling the balancer prevents the cluster from redistributing data, which leads to hotspots. While it can be scheduled for off-peak hours, disabling it indefinitely causes severe performance issues as the data distribution becomes increasingly skewed, ultimately bottlenecking the entire database architecture.
- ✗
Using the same shard key for every collection in the database.
Why it's wrong here
Choosing the best shard key depends on the access patterns and data distribution of each individual collection. Forcing a single key for all collections can lead to suboptimal performance for specific queries and does not account for the varying requirements of different application datasets.
About these practice questions
Courseiva writes every C100DBA question from scratch — 222 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
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.