DP-300 Practice Question: Monitor, configure, and optimize database resources
This DP-300 practice question tests your understanding of monitor, configure, and optimize database resources. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are monitoring an Azure SQL Database using Query Performance Insight. You see a query with high duration and high CPU usage. The query plan shows a clustered index scan. What is the most likely cause and recommendation?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Missing nonclustered index; create an index on the predicates.
Query Performance Insight shows a query with high duration and CPU usage, and the query plan reveals a clustered index scan. A clustered index scan reads all rows in the table, which is inefficient when only a subset of rows is needed. The most likely cause is a missing nonclustered index on the columns used in the WHERE clause (predicates), which would allow a seek operation instead of a full scan, reducing both CPU and duration.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Fragmented clustered index; rebuild the clustered index.
Why it's wrong here
Fragmentation causes scans but not necessarily high CPU; missing index is more likely.
✗
Insufficient memory; increase the service tier.
Why it's wrong here
Memory pressure might cause scans, but missing index is a common cause.
✓
Missing nonclustered index; create an index on the predicates.
Why this is correct
An index seek would reduce CPU and duration.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Parameter sniffing; add OPTION (RECOMPILE).
Why it's wrong here
Parameter sniffing causes varying plans, not necessarily scans.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse a clustered index scan with fragmentation or parameter sniffing, but the scan is a symptom of a missing nonclustered index that would allow a seek, not a problem with the clustered index itself or plan caching.
Detailed technical explanation
How to think about this question
A clustered index scan is equivalent to a table scan on a heap when the clustered index is not used for seeking; it reads all leaf-level pages. Creating a covering nonclustered index on the predicate columns (e.g., WHERE column = value) enables an index seek, which reads only the relevant rows. In Azure SQL Database, Query Performance Insight can directly recommend missing indexes via the 'Missing Index Details' link in the query plan, and the database engine tracks missing index impact using DMVs like sys.dm_db_missing_index_details.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this DP-300 question in full detail.
Monitor, configure, and optimize database resources — This question tests Monitor, configure, and optimize database resources — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Missing nonclustered index; create an index on the predicates. — Query Performance Insight shows a query with high duration and CPU usage, and the query plan reveals a clustered index scan. A clustered index scan reads all rows in the table, which is inefficient when only a subset of rows is needed. The most likely cause is a missing nonclustered index on the columns used in the WHERE clause (predicates), which would allow a seek operation instead of a full scan, reducing both CPU and duration.
What should I do if I get this DP-300 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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