C100DBA Indexing and Performance Practice Question
Why should you avoid creating too many indexes on a single collection?
⚠ Common exam trap
Many students mistakenly believe that more indexes only impact disk space, forgetting the significant performance penalty excessive indexes impose on writes and memory usage.
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
✓
It increases the cost of write operations.
Every index adds overhead to every write operation (insert, update, delete) because the database must maintain the index structure alongside the collection. Furthermore, indexes consume significant memory, and if the working set (the data and indexes most frequently accessed) exceeds available RAM, the database will experience frequent page faults from disk, leading to severe performance degradation across all types of operations.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It prevents the use of sharding.
Why it's wrong here
The number of indexes on a collection has no impact on the ability to shard the data. Sharding is a structural choice based on the shard key, which is independent of the number of local indexes on a collection. You can have many indexes on a sharded collection.
- ✓
It increases the cost of write operations.
Why this is correct
Each index must be updated whenever a document is inserted, modified, or deleted. Maintaining these B-trees adds synchronous I/O overhead to every write, which can create significant latency and limit the write throughput of the application as the number of indexes grows on the collection.
- ✗
It automatically disables the WiredTiger cache.
Why it's wrong here
Indexes do not disable the WiredTiger cache. In fact, indexes are intended to be cached in RAM to provide fast performance. The issue with too many indexes is not the cache itself, but the memory pressure caused by the indexes competing for space within that cache.
- ✗
It forces queries to use a collection scan.
Why it's wrong here
Having too many indexes does not force a collection scan; in fact, it provides more options for the optimizer. The issue is that the optimizer might take longer to evaluate all potential plans, and the storage overhead negatively impacts overall system performance, not that it forces scans.
About these practice questions
One of 222 original C100DBA practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. 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.