The answer is to reorganize the clustered columnstore index. This is the correct action because, over time, data modifications like inserts, updates, and deletes cause fragmentation in the columnstore, creating small or partially deleted rowgroups that degrade scan efficiency. Reorganizing physically recompresses these rowgroups, removes deleted rows, and merges small groups, directly improving query performance on large fact tables in Synapse Analytics. On the DP-900 exam, this concept tests your understanding of maintaining columnstore index health as part of data warehouse optimization—a common trap is confusing reorganize with rebuild, but reorganize is less resource-intensive and sufficient for moderate fragmentation. Remember the memory tip: "Reorganize to reorganize rowgroups, rebuild only when you need a full reset."
DP-900 Practice Question: Identify considerations for relational data on Azure
This DP-900 practice question tests your understanding of identify considerations for relational data on azure. 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.
A data warehouse team in Azure Synapse Analytics notices query performance degradation on a large fact table. The table is partitioned by date and has a clustered columnstore index. Which action is most likely to improve performance?
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
✓
Reorganize the clustered columnstore index
Reorganizing the clustered columnstore index (option C) is the most likely action to improve performance because, over time, columnstore indexes can become fragmented due to data modifications (inserts, updates, deletes). Reorganizing the index physically recompresses the data into optimal rowgroups, removing deleted rows and merging small rowgroups, which directly improves query scan efficiency and reduces I/O.
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.
✗
Update statistics on the fact table
Why it's wrong here
Updating statistics helps the query optimizer but may not resolve index fragmentation.
✗
Drop and recreate the partition boundaries
Why it's wrong here
This does not address index fragmentation and may cause data movement.
✓
Reorganize the clustered columnstore index
Why this is correct
Reorganizing compresses and merges columnstore segments, improving query performance.
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.
✗
Change the distribution to ROUND_ROBIN
Why it's wrong here
Changing distribution requires table rebuild and may not help with index fragmentation.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse index maintenance (reorganize/rebuild) with statistics updates or distribution changes, mistakenly believing that stale statistics or a different distribution method are the primary causes of performance degradation on a large, partitioned fact table with a clustered columnstore index.
Detailed technical explanation
How to think about this question
Columnstore indexes store data in compressed column segments called rowgroups, each ideally containing 1,048,576 rows. Fragmentation occurs when rowgroups are not fully compressed (e.g., after bulk inserts) or when deleted rows leave gaps. The ALTER INDEX REORGANIZE command in Azure Synapse Analytics forces a background process to recompress and merge rowgroups, restoring optimal compression and scan performance without blocking concurrent queries, unlike a full rebuild.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this DP-900 question in full detail.
Identify considerations for relational data on Azure — This question tests Identify considerations for relational data on Azure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Reorganize the clustered columnstore index — Reorganizing the clustered columnstore index (option C) is the most likely action to improve performance because, over time, columnstore indexes can become fragmented due to data modifications (inserts, updates, deletes). Reorganizing the index physically recompresses the data into optimal rowgroups, removing deleted rows and merging small rowgroups, which directly improves query scan efficiency and reduces I/O.
What should I do if I get this DP-900 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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