20+ practice questions focused on Indexing and Performance — one of the most tested topics on the MongoDB Certified DBA Associate exam. Each question includes a detailed explanation so you learn why the right answer is correct.
Start Indexing and Performance PracticeRefer to the exhibit. Why is the query execution plan performing a FETCH stage after an IXSCAN, and how can it be optimized?
Explanation: The FETCH stage indicates that the index used (status, type) does not contain the 'created' field, forcing MongoDB to load documents from disk to sort them in memory. This is a common performance bottleneck. Adding the 'created' field to the index as the third key will allow an index-based sort, enabling the query to be covered by the index and eliminating the expensive blocking sort and fetch operations.
Which TWO of the following statements regarding the TTL (Time-To-Live) index are correct?
Explanation: TTL indexes are a specialized feature used to automatically remove documents from a collection after a specific duration. They are crucial for managing temporary data like sessions or logs. Understanding their constraints—such as not being compatible with capped collections and the approximate nature of the deletion process—is fundamental for ensuring data lifecycle management is handled correctly within the database.
Which THREE factors significantly impact the performance of a MongoDB write operation?
Explanation: Write performance is influenced by several architectural factors. Index overhead is primary, as every write requires updating all relevant indexes. Replication lag affects write concern acknowledgement, and disk I/O latency limits the throughput of the storage engine. Understanding how these factors interact allows developers and DBAs to tune write concerns and index counts to meet the specific throughput and latency requirements of their applications.
Refer to the exhibit. A query filters on field 'a'. Which index will the optimizer choose?
Explanation: MongoDB's query optimizer evaluates available indexes based on cost. When both {a: 1, b: 1} and {a: 1} are available, both can satisfy a query filtering on 'a'. However, the optimizer typically prefers the index that is most specific or smaller if the costs are identical. In many cases, the single-field index {a: 1} is preferred as it is smaller and more efficient for a single-field filter.
What happens when a $sort operation cannot be satisfied by an index?
Explanation: If a query result set exceeds the 100 MB limit for an in-memory sort, MongoDB will throw an error and terminate the query. When sorting is required but no index can provide the order, MongoDB must perform a blocking sort in memory. This is a common performance trap that often leads to high memory consumption and application errors if the collection grows significantly larger than expected.
+15 more Indexing and Performance questions available
Practice all Indexing and Performance questions1. Baseline your knowledge
Start with 10 questions to gauge your current understanding of Indexing and Performance. This tells you whether you need a concept refresher or just practice.
2. Review every explanation
For each question — right or wrong — read the full explanation. Understanding why an answer is correct is more valuable than knowing the answer itself.
3. Focus on exam traps
Indexing and Performance questions on the C100DBA frequently use trap wording. Look for subtle differences in answers that test your precision, not just general knowledge.
4. Reach 80% consistently
Do repeated sessions until you score 80%+ three times in a row. Then move to mixed-mode practice to test cross-topic recall under realistic conditions.
The exact number varies per candidate. Indexing and Performance is tested as part of the MongoDB Certified DBA Associate blueprint. Practicing with targeted Indexing and Performance questions ensures you can handle any format or difficulty that appears.
Yes. Courseiva provides free C100DBA practice questions across all exam topics and domains. The platform includes topic-based practice, mock exams, missed-question review, bookmarked questions, and readiness tracking — no account required.
Difficulty is subjective, but Indexing and Performance is a high-priority exam concept tested in multiple ways — direct recall, scenario analysis, and command-output interpretation. Consistent practice is the best way to build confidence.
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