C100DBA Application Administration Practice Question
An application is using a capped collection for logging. What happens when the collection reaches its configured size limit?
⚠ Common exam trap
Candidates frequently mistake capped collections for fixed-size files that stop accepting writes once full. They fail to realize the database automatically overwrites the oldest data to maintain the limit.
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
✓
The oldest documents are overwritten by new inserts.
Capped collections follow a 'first-in, first-out' pattern where the oldest documents are automatically overwritten to maintain the specified size. This fixed-size behavior ensures that logging collections do not consume infinite disk space, which is critical for system stability. Application administrators must account for this behavior when designing log management, as it prevents the need for manual cleanup scripts while ensuring the database only retains the most recent relevant operational data for the application.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The collection automatically expands to accommodate new data.
Why it's wrong here
Capped collections are created with a fixed size and cannot grow beyond their defined limit. This is a deliberate design feature meant to provide predictable performance and storage footprint, and any attempt to exceed the cap results in the removal of the oldest data to make room for new records.
- ✗
The database throws a 'CollectionFull' error for new inserts.
Why it's wrong here
Capped collections are designed to handle high-frequency writes by rotating storage. They do not stop accepting writes when full; instead, they automatically overwrite the oldest records in the collection to ensure the application continues logging without encountering write errors or needing intervention to manage the collection's data volume.
- ✓
The oldest documents are overwritten by new inserts.
Why this is correct
Capped collections maintain a circular buffer structure. Once the defined size limit or maximum document count is reached, the database automatically removes the oldest documents to make space for incoming data. This process is seamless and allows the application to maintain a constant, manageable storage footprint for its data.
- ✗
All existing documents are deleted to free up space.
Why it's wrong here
Deleting the entire collection would be counterproductive for a log stream. Capped collections are designed for continuous data ingestion, and they manage their size by selectively removing only the oldest entries rather than clearing the entire dataset, which would cause an unnecessary loss of recent operational data logs.
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.