C100DEV Indexing Practice Question
What is the primary consequence of having too many indexes on a collection that experiences a high volume of write operations?
⚠ Common exam trap
Candidates often think extra indexes only consume disk space, failing to realize the significant performance tax on write operations caused by constant index updates (write amplification).
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
✓
Decreased performance of write operations.
Every index on a collection must be updated whenever a document is inserted, updated, or deleted. In write-heavy workloads, this results in significant write amplification. Each write operation triggers multiple index update tasks, consuming CPU and I/O resources. Maintaining excessive indexes leads to performance degradation as the system struggles to keep all indexes synchronized with the base data, directly impacting latency and throughput for application-level database interactions.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increased disk space usage for data storage.
Why it's wrong here
While indexes do consume disk space, the primary concern for write-heavy workloads is the performance overhead of maintaining those structures. Disk space is a secondary storage concern, whereas the CPU and I/O latency introduced by constant index updates during every write operation is the immediate bottleneck for application performance.
- ✓
Decreased performance of write operations.
Why this is correct
Write performance suffers because each index must be updated synchronously during document modifications. As the count of indexes grows, the number of operations per write increases, creating a bottleneck that slows down the ingestion of data and negatively impacts the overall latency of the application's write-intensive processes.
- ✗
Increased memory usage for query execution.
Why it's wrong here
Indexes are generally used for read operations to speed up filtering. While having many indexes might affect the WiredTiger cache efficiency, the direct consequence of write-heavy workloads is the immediate penalty paid during the insertion or update process, not necessarily an increase in memory usage for query execution tasks.
- ✗
Improved speed for data deletion operations.
Why it's wrong here
Data deletion actually becomes slower with more indexes. When a document is removed, every index containing that document must also be updated to remove the corresponding entry. This adds overhead to the deletion process, contrary to the idea that it would improve speed for such operations within the collection.
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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
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