DBS-C01 Monitoring and Troubleshooting Practice Question
A company runs a document database using Amazon DocumentDB. They notice that some queries are taking much longer than expected. The explain plan shows a COLLSCAN. Which action would most improve query performance?
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
✓
Create appropriate indexes on the fields used in query filters
Creating appropriate indexes on the fields used in query filters is the most effective action to improve performance because it eliminates the need for a COLLSCAN (collection scan). Increasing instance size (option A) may help but does not address the root cause of missing indexes. Changing read consistency from eventual to strong (option B) affects the freshness of reads, not query performance. Increasing storage (option C) does not improve query speed; it only provides more space for data.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the instance size to the next tier
Why it's wrong here
Scaling up provides more resources but doesn't fix the missing index.
- ✗
Change the read consistency from eventual to strong
Why it's wrong here
Consistency level does not affect scan vs. index.
- ✗
Increase the storage allocated to the instance
Why it's wrong here
Storage increase does not impact query execution speed.
- ✓
Create appropriate indexes on the fields used in query filters
Why this is correct
Indexes prevent full collection scans.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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